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TWENTIETH   CENTURY  TEXT-BOOKS 

EDITED    BY 

A.   F.  NIGHTINGALE,   Ph.D.,   LL.D. 

SUPERINTENDENT   OF  SCHOOLS,    COOK    COUNTY,    ILLINOIS 


TWENTIETH    CENTURY   TEXT-BOOKS 


PLANT  STRUCTURES 

A  SECOND   BOOK  OF  BOTANY 


BY 

JOHN   M.   COULTER,   A.M.,   Ph.D. 

HEAD    OF    DEPARTMENT   OF   BOTANY 
UNIVERSITY    OF   CHICAGO 


SECOND   EDITION  REVISED 


NEW    YORK 

D.   APPLETON    AND    COMPANY 

1904 


Copyright,  1899,  1904, 
By  D.  APPLETON  AND  COHIPANY. 


PKEFACE 

In  the  preface  to  Plant  Relations  the  author  gave  his 
reasons  for  suggesting  that  the  ecological  standpoint  is  best 
adapted  for  the  first  contact  with  plants.  It  may  be,  how- 
ever, that  many  teachers  will  prefer  to  begin  with  the  mor- 
phological standpoint,  as  given  in  the  present  book.  Rec- 
ognizing this  fact,  Plant  Structures  has  been  made  an 
independent  volume  that  may  precede  or  follow  the  other, 
or  may  provide  a  brief  course  of  botanical  study  in  itself. 

Although  in  the  present  volume  Morphology  is  the  domi- 
nant subject,  it  seems  wise  to  give  a  somewhat  general  view 
of  plants,  and  therefore  Physiology,  Ecology,  and  Taxonomy 
are  included  in  a  general  way.  For  fear  that  Physiology 
and  Ecology  may  be  lost  sight  of  as  distinct  subjects,  and 
to  introduce  important  topics  not  included  in  the  body  of 
the  work,  short  chapters  are  devoted  to  them,  which  seek 
to  bring  together  the  main  facts,  and  to  call  attention  to 
the  larger  fields. 

This  book  is  not  a  laboratory  guide,  but  is  for  reading 
and  study  in  connection  with  laboratory  ivorTc.  An  accom- 
panying pamphlet  for  teachers  gives  helpful  suggestions 
to  those  who  are  not  already  familiar  with  its  scope  and 
purpose.  It  is  not  expected  that  all  the  forms  and  sub- 
jects presented, in  the  text  can  be  included  in  the  labora- 
tory exercises^  but  it  is  believed  that  the  book  will  prove  a 
useful  companion  in  connection  with  such  exercises.  It 
is  very  necessary  to  co-ordinate  the  results  of  laboratory 
work,  to  refer  to  a  larger  range  of  material  than  can  be 
handled,  and  to  develop  some  philosophical  conception  of 


yi  PREFACE 

the  plant  kingdom.  The  learning  of  methods  and  the 
collection  of  facts  are  fundamental  processes,  but  they 
must  be  supplemented  by  information  and  ideas  to  be  of 
most  service. 

The  author  does  not  believe  in  the  use  of  technical 
terms  unless  absolutely  necessary,  for  they  lead  frequently 
to  mistaking  definitions  of  words  for  knowledge  of  things. 
But  it  is  necessary  to  introduce  the  student  not  merely  to 
the  main  facts  but  also  to  the  literature  of  botany.  Ac- 
cordingly, the  most  commonly  used  technical  terms  are 
introduced,  often  two  or  three  for  the  same  thing,  but  it 
is  hoped  that  familiarity  with  them  will  enable  the  student 
to  read  any  ordinary  botanical  text.  Care  has  been  taken 
to  give  definitions  and  derivations,  and  to  call  repeated 
attention  to  synonymous  terms,  so  that  there  may  be  no 
confusion.  The  chaotic  state  of  morphological  terminology 
tempted  the  author  to  formulate  or  accept  some  consistent 
scheme  of  terms  ;  but  it  was  felt  that  this  would  impose 
upon  the  student  too  great  difficulty  in  reading  far  more 
important  current  texts. 

Chapters  I-XII  form  a  connected  whole,  presenting  the 
general  story  of  the  evolution  of  plants  from  the  lowest  to 
the  highest.  The  remaining  chapters  are  supplementary, 
and  can  be  used  as  time  or  inclination  permits,  but  it  is  the 
judgment  of  the  author  that  they  should  be  included  if 
possible.  The  flower  is  so  conspicuous  and  important  a 
feature  in  connection  with  the  highest  plants,  that  Chapter 
XlII  seems  to  be  a  fitting  sequel  to  the  preceding  chapters. 
It  also  seems  desirable  to  develop  some  knowledge  of  the 
great  Angiosperm  families,  as  presented  in  Chapter  XIV, 
since  they  are  the  most  conspicuous  members  of  every  flora. 
In  this  connection,  the  author  has  been  in  the  habit  of 
directing  the  examination  of  characteristic  flowers,  and  of 
teaching  the  use  of  ordinary  taxonomic  manuals.  Chap- 
ter XV  deals  with  anatomical  matters,  but  the  structures 
included  are  so  bound  up  with  the  form  and  work  of  plants 


PREFACE  yji 

that  it  seems  important  to  find  a  place  for  them  even  in  an 
elementary  work.  The  reason  for  Chapters  XVI  and  XVII 
has  been  stated  already,  and  even  if  Plant  Relations  is  stud- 
ied, Chapter  XVII  will  be  useful  either  as  a  review  or  as  an 
introduction.  In  the  chapter  on  Plant '  Physiology  the 
author  has  been  guided  by  Xoll's  excellent  resume  in  the 
"  Strasburger  "  Botany. 

The  illustrations  have  been  entirely  in  the  charge  of 
Dr.  Otis  W.  Caldwell,  who  for  several  years  has  conducted 
in  the  University,  and  in  a  most  efficient  way,  such  labo- 
ratory work  as  this  volume  implies.  Many  original  illus- 
trations have  been  prepared  by  him,  and  under  his  direction 
by  Messrs.  S.  M.  Coulter,  B.  A,  Goldberger,  W.  J.  G.  Land, 
and  A.  0.  Moore,  and  some  are  credited  to  Dr.  Chamberlain 
and  Dr.  Cowles,  of  the  University,  but  it  is  a  matter  of 
regret  that  pressure  of  work  and  time  limitation  have  for- 
bidden a  still  greater  number.  The  authors  of  the  original 
illustrations  are  cited,  and  where  illustrations  have  been 
obtained  elsewhere  the  sources  are  indicated. 

The  author  would  again  call  attention  to  the  fact  that 
this  book  is  merely  intended  to  serve  as  a  compact  supple- 
ment to  three  far  more  important  factors :  the  teacher,  the 
laboratory,  a?id  field  work.  John  M.  Coulter. 

TuE  UxivERSiTY  OF  CHICAGO,  November,  1899. 

PREFACE   TO   THE   REVISED   EDITI0:N^ 

During  the  last  five  years  the  science  of  Botany  has 
made  rapid  progress,  both  in  the  addition  of  new  facts  and 
in  changed  points  of  view.  Some  of  this  progress  affects 
Plant  Structures^  and  it  is  recorded  in  this  revised  edition 
so  far  as  it  can  be  without  a  complete  rewriting  of  the 
volume.  Changes  will  be  found,  therefore,  in  statements 
of  fact,  in  points  of  view,  in  terminology,  in  illustrations, 
and  also  in  the  addition  of  new  material. 

John  M.  Coulter. 
Tns  University  of  Chicago,  April,  1904. 


CONTENTS 

CHAPTER  PAGE 

I. — Introduction =        .        .  1 

II. — Thallophytes  :  Alg^ 4 

III. — The  evolution  of  sex 13 

IV. — The  great  groups  of  Alg^     ...                .        .  17 

V. — Thallophytes:  Fungi 48 

VI. — The  food  of  plants 83 

VII. — Bryophytes 93 

VIII. — The  great  groups  of  Bryophytes 109 

IX. — Pteridophytes 128 

X. — The  great  groups  of  Pteridophytes      ....  155 

XI. — Spermatophytes  :  Gymnosperms 171 

XII. — Spermatophytes  :  Angiosperms 195 

XIII. — The  flower 218 

XIV. — Monocotyledons  and  dicotyledons 232 

XV. — Differentiation  of  tissues 280 

XVI. — Plant  physiology 297 

XVII, — Plant  ecology 311 

Glossary 329 

Index 337 

ix 


BOTANY 

PART    II.— PLANT    STRUCTURES 


CHAPTER    I 

INTRODUCTION 

1.  Differences  in  structure. — It  is  evident,  even  to  the 
casual  observer,  that  plants  differ  very  much  in  structure. 
They  differ  not  merely  in  form  and  size,  but  also  in  com- 
plexity. Some  plants  are  simple,  others  are  complex,  and 
the  former  are  regarded  as  of  lower  rank. 

Beginning  with  the  simplest  plants — that  is,  those  of 
lowest  rank — one  can  pass  by  almost  insensible  grada- 
tions to  those  of  highest  rank.  At  certain  points  in  this 
advance  notable  interruptions  of  the  continuity  are  dis- 
covered, structures,  and  hence  certain  habits  of  work,  chang- 
ing decidedly,  and  these  breaks  enable  one  to  organize  the 
vast  array  of  plants  into  groups.  Some  of  the  breaks  ap- 
pear to  be  more  important  than  others,  and  opinions  may 
differ  as  to  those  of  chief  importance,  but  it  is  customary 
to  select  three  of  them  as  indicating  the  division  of  the 
plant  kingdom  into  four  great  groups. 

2.  The  great  groups. — The  four  great  groups  may  be 
indicated  here,  but  it  must  be  remembered  that  their  names 
mean  nothing  until  plants  representing  them  have  been 
studied.     It  will  be  noticed  that  all  the  names  have  the 

1 


2  PLANT   STKUCTURES 

constant  termination  phytes^  which  is  a  Greek  word  mean- 
ing "  plants."  The  prefix  in  each  case  is  also  a  Greek  word 
intended  to  indicate  the  kind  of  plants. 

(1)  Thallophytes. — The  name  means  "thallus  plants," 
but  just  what  a  "  thallus "  is  can  not  well  be  explained 
until  some  of  the  plants  have  been  examined.  In  this 
great  group  are  included  some  of  the  simplest  forms, 
known  as  Algce  and  Fu7igi,  the  former  represented  by  green 
thready  growths  in  fresh  water  and  the  great  host  of  sea- 
weeds, the  latter  by  moulds,  mushrooms,  etc. 

(2)  Bryophytes.— The  name  means  "  moss  plants,"  and 
suggests  very  definitely  the  forms  which  are  included. 
Every  one  knows  mosses  in  a  general  way,  but  associated 
with  them  in  this  great  group  are  the  allied  liverworts, 
which  are  very  common  but  not  so  generally  known. 

(3)  Pteridophytes. — The  name  means  "  fern  plants,"  and 
ferns  are  well  known.  Not  all  Pteridophytes,  however,  are 
ferns,  for  associated  with  them  are  the  horsetails  (scouring 
rushes)  and  the  club  mosses. 

(4)  Spermatophytes. — The  name  means  "  seed  plants  " — 
that  is,  those  plants  which  produce  seeds.  In  a  general 
way  these  are  the  most  familiar  plants,  and  are  commonly 
spoken  of  as  "  flowering  plants."  They  are  the  highest  in 
rank  and  the  most  conspicuous,  and  hence  have  received 
much  attention.  In  former  times  the  study  of  botany  in 
the  schools  was  restricted  to  the  examination  of  this  one 
group,  to  the  entire  neglect  of  the  other  three  great  groups. 

3.  Increasing  complexity. — At  the  very  outset  it  is  well 
to  remember  that  the  Thallophytes  contain  the  simplest 
plants — those  whose  bodies  have  developed  no  organs  for 
special  work,  and  that  as  one  advances  through  higher 
Thallophytes,  Bryophytes,  and  Pteridophytes,  there  is  a  con- 
stant increase  in  the  complexity  of  the  plant  body,  until  in 
the  Spermatophytes  it  becomes  most  highly  organized,  with 
numerous  structures  set  apart  for  special  work,  just  as  in  the 
highest  animals  limbs,  eyes,  ears,  bones,  muscles,  nerves,  etc., 


INTRODUCTION  3 

are  set  apart  for  special  work.  The  increasing  complexity 
is  usually  spoken  of  as  differentiatio7i — that  is,  the  setting 
apart  of  structures  for  different  kinds  of  work.  Hence  the 
Bryophytes  are  said  to  be  more  highly  differentiated  than 
the  Thallophytes,  and  the  Spermatophytes  are  regarded  as 
the  most  highly  differentiated  group  of  plants. 

4.  Nutrition  and  reproduction. — However  variable  plants 
may  be  in  complexity,  they  all  do  the  same  general  kind  of 
work.  Increasing  complexity  simply  means  an  attempt  to 
do  this  work  more  effectively.  It  is  plant  work  that  makes 
plant  structures  significant,  and  hence  in  this  book  no  at- 
tempt will  be  made  to  separate  them.  All  the  work  of 
plants  may  be  put  under  two  heads,  nutrition  and  repro- 
duction, the  former  including  all  those  processes  by  which 
a  plant  maintains  itself,  the  latter  those  processes'  by  which 
it  produces  new  plants.  In  the  lowest  plants,  these  two 
great  kinds  of  work,  or  functions,  as  they  are  called,  are 
not  set  apart  in  different  regions  of  the  body,  but  usually 
the  first  step  toward  differentiation  is  to  set  apart  the  re- 
productive function  from  the  nutritive,  and  to  develop 
special  reproductive  organs  which  are  entirely  distinct  from 
the  general  nutritive  body. 

5.  The  evolution  of  plants.— It  is  generally  supposed  that 
the  more  complex  plants  have  descended  from  the  simpler 
ones ;  that  the  Bryophytes  have  been  derived  from  the  Thallo- 
phytes, and  so  on.  All  the  groups,  therefore,  are  supposed 
to  be  related  among  themselves  in  some  way,  and  it  is  one 
of  the  great  problems  of  botany  to  discover  these  relation- 
ships. This  theory  of  the  relationship  of  plant  groups  is 
known  as  the  theori/  of  descent,  or  more  generally  as  evo- 
lution. To  understand  any  higher  group  one  must  study 
the  lower  ones  related  to  it,  and  therefore  the  attempt  of 
this  book  will  be  to  trace  the  evolution  of  the  plant  king- 
dom, by  beginning  with  the  simplest  forms  and  noting  the 
gradual  increase  in  complexity  until  the  highest  forms  are 
reached. 


CHAPTEE  II 

THALLOPHYTES  :  ALG-Sl 

6.  General  characters. — Thallophytes  are  the  simplest  of 
plants,  often  so  small  as  to  escape  general  observation,  but 
sometimes  with  large  bodies.  They  occur  everywhere  in 
large  numbers,  and  are  of  special  interest  as  representing 
the  beginnings  of  the  plant  kingdom.  In  this  group  also 
there  are  "organized  all  of  the  principal  activities  of  plants, 
so  that  a  study  of  Thallophytes  furnishes  a  clew  to  the 
structures  and  functions  of  the  higher,  more  complex 
groups. 

The  word  "  thallus "  refers  to  the  nutritive  body,  or 
vegetative  body,  as  it  is  often  called.  This  body  does  not 
differentiate  special  nutritive  organs,  such  as  the  leaves  and 
roots  of  higher  plants,  but  all  of  its  regions  are  alike.  Its 
natural  position  also  is  not  erect,  but  prone.  While  most 
Thallopliytes  have  thallus  bodies,  in  some  of  them,  as  in 
certain  marine  forms,  the  nutritive  body  differentiates  into 
regions  which  resemble  leaves,  stems,  and  roots  ;  also  cer- 
tain Bryophytes  have  thallus  bodies.  The  thallus  body, 
therefore,  is  not  always  a  distinctive  mark  of  Thallophytes, 
but  must  be  supplemented  by  other  characters  to  determine 
the  group. 

7.  Algae  and  Fungi.— It  is  convenient  to  separate  Thallo- 
phytes into  two  great  divisions,  known  as  AlgcB  and  Fungi. 
It  should  be  known  that  this  is  a  very  general  division  and 
not  a  technical  one,  for  there  are  groups  of  Thallophytes 
which  can  not  be  regarded  as  strictly  either  Algte  or  Fungi, 
but  for  the  present  these  groups  may  be  included. 

4 


THALLOPHYTES:  ALG^  5 

The  great  distinction  between  these  two  divisions  of 
Thallophytes  is  that  the  Algae  contain  chlorophyll  and  the 
Fungi  do  not.  Chlorophyll  is  the  characteristic  green  color- 
ing matter  found  in  plants,  the  word  meaning  "  leaf  green," 
It  may  be  thought  that  to  use  this  coloring  material  as  the 
basis  of  such  an  important  division  is  somewhat  superficial, 
but  it  should  be  known  that  the  presence  of  chlorophyll  gives 
a  peculiar  power — one  which  affects  the  whole  structure 
of  the  nutritive  body  and  the  habit  of  life.  The  presence 
of  chlorophyll  means  that  the  plant  can  make  its  own  food, 
can  live  independent  of  other  plants  and  animals.  Algae, 
therefore,  are  the  independent  Thallophytes,  so  far  as  their 
food  is  concerned,  for  they  can  manufacture  it  out  of  the 
inorganic  materials  about  them. 

The  Fungi,  on  the  other  hand,  contain  no  chlorophyll, 
can  not  manufacture  food  from  inorganic  material,  and 
hence  must  obtain  it  already  manufactured  by  plants  or 
animals.  In  this  sense  they  are  dependent  upon  other  or- 
ganisms, and  this  dependence  has  led  to  great  changes  in 
structure  and  habit  of  life. 

It  is  supposed  that  Fungi  have  descended  from  Algae — 
that  is,  that  they  were  once  Alg^e,  which  gradually  acquired 
the  habit  of  obtaining  food  already  manufactured,  lost  their 
chlorophyll,  and  became  absolutely  dependent  and  more  or 
less  modified  in  structure.  Fungi  may  be  regarded,  there- 
fore, as  reduced  relatives  of  the  Algfe,  of  equal  rank  so  far 
as  birth  and  structure  go,  but  of  very  different  habits. 

ALG^ 

8.  General  characters. — As  already  defined.  Algae  are 
Thallophytes  which  contain  chlorophyll,  and  are  therefore 
able  to  manufacture  food  from  inorganic  material.  They 
are  known  in  general  as  "  seaweeds,"  although  there  are 
fresh-water  forms  as  well  as  marine.  They  are  exceedingly 
variable  in  size,  ranging  from  forms  visible  only  by  means 
19 


Q  PLANT   STRUCTURES 

of  the  compound  microscope  to  marine  forms  with  enor- 
mously bulky  bodies.  In  general  they  are  hydrophytes — that 
is,  plants  adapted  to  life  in  water  or  in  very  moist  places. 
The  special  interest  connected  with  the  group  is  that  it  is 
supposed  to  be  the  ancestral  group  of  the  plant  kingdom — 
the  one  from  which  the  higher  grou2)s  have  been  more  or 
less  directly  derived.  In  this  regard  they  differ  from  the 
Fungi,  which  are  not  supposed  to  be  responsible  for  any 
higher  groups. 

9.  The  subdivisions. — Although  all  the  Alg^e  contain 
chlorophyll,  some  of  them  do  not  appear  green.  In  some 
of  them  another  coloring  matter  is  associated  with  the  chlo- 
rophyll and  may  mask  it  entirely.  Advantage  is  taken  of 
these  color  associations  to  separate  Algge  into  subdivisions. 
As  these  colors  are  accompanied  by  constant  differences  in 
structure  and  work,  the  distinction  on  the  basis  of  colors  is 
more  real  than  it  might  appear.  Upon  this  basis  four  sub- 
divisions may  be  made.  The  constant  termination  phycecB, 
which  appears  in  the  names,  is  a  Greek  word  meaning  "  sea- 
w^eed,"  which  is  the  common  name  for  Algse  ;  while  the  pre- 
fix in  each  case  is  the  Greek  name  for  the  color  which  char- 
acterizes the  group. 

The  four  subdivisions  are  as  follows  :  (1)  Cyanopliycem, 
or  "  Blue  Algas,"  but  usually  called  "  Blue-green  Alga3,"  as  the 
characteristic  blue  does  not  entirely  mask  the  green,  and 
the  general  tint  is  bluish-green ;  (2)  Chlorophycece,  or  "  Green 
Algge,"  in  which  there  is  no  special  coloring  matter  associ- 
ated with  the  chlorophyll ;  (3)  Phceophycece.,  or  "  Brown 
Algae  " ;  and  (4)  Rhodojjhycece,  or  "  Eed  Algge." 

It  should  be  remarked  that  probably  the  Cyanophyceas 
do  not  belong  with  the  other  groups,  but  it  is  convenient  to 
present  them  in  this  connection. 

10.  The  plant  body. — By  this  phrase  is  meant  the  nutri- 
tive or  vegetative  body.  There  is  in  plants  a  unit  of  struc- 
ture known  as  the  cell.  The  bodies  of  the  simplest  plants 
consist  of  but  one  cell,  while  the  bodies  of  the  most  com- 


TIIALLOIMIYTES:   ALG.E 


plex  plants  consist  of  very  many  cells.  It  is  necessary  to 
know  something  of  the  ordinary  living  plant  cell  before  the 
bodies  of  Alga?  or  any  other  2)lant  bodies  can  be  under- 
stood. 

Such  a  cell  if  free  is  approximately  spherical  in  outline, 
(Fig.  6),  but  if  pressed  upon  by  contiguous  cells  may  become 
variously  modified  in  form 
(Fig.  1).  Bounding  it  there 
is  a  thin,  elastic  wall,  com- 
posed of  a  substance  called 
cellulose.  The  cell  wall, 
therefore,  forms  a  delicate 
sac,  which  contains  the  liv- 
ing substance  known  as  pro- 
toplasm. This  is  the  sub- 
stance which  manifests  life, 
and  is  the  only  substance 
in  the  plant  which  is  alive. 
It  is  the  protoplasm  which 
has  organized  the  cellulose 
wall  about  itself,  and  which 
does  all  the  plant  work.  It 
is  a  fluid  substance  which 
varies  much  in  its  consistence,  sometimes  being  a  thin  vis- 
cous fluid,  like  the  white  of  an  egg,  sometimes  much  more 
dense  and  compactly  organized. 

The  protophism  of  the  cell  is  organized  into  various 
structures  which  are  called  organs  of  the  cell,  each  organ 
having  one  or  more  special  functions.  One  of  the  most 
conspicuous  organs  of  the  living  cell  is  the  single  nucleus, a, 
comparatively  compact  and  usually  spherical  protoplasmic 
body,  and  generally  centrally  placed  within  the  cell  (Fig.  1). 
All  about  the  nucleus,  and  filling  up  the  general  cavity 
within  the  cell  wall,  is  an  organized  mass  of  much  thinner 
protoplasm,  known  as  cytoplasm.  The  cytoplasm  seems  to 
form  tlie  general  background  or  matrix  of  the  cell,  and  the 


Fig.    1.      t^-\U    fruui    a   ui...-^    Kaf,  r.l,..uu.s 

nucleus  (B)  in  which  there  is  a  nucle- 
olus, cytoplasm  (C),  and  chloroplasts 
(^4 ). — Caldwell. 


8  PLANT  STRUCTUKES 

nucleus  lies  imbedded  within  it  (Fig.  1).  Every  working 
cell  consists  of  at  least  cytoplasm  and  nucleus.  Sometimes 
the  cellulose  wall  is  absent,  and  the  cell  then  consists  sim- 
ply of  a  nucleus  with  more  or  less  cytoplasm  organized 
about  it,  and  is  said  to  be  naked. 

Another  protoplasmic  organ  of  the  cell,  very  conspicuous 
among  the  Algaj  and  other  groups,  is  the  plastid.  Plastids 
are  relatively  compact  bodies,  commonly  spherical,  variable 
in  number,  and  lie  imbedded  in  the  cytoplasm.  There  are 
various  kinds  of  plastids,  the  most  common  being  the  one 
which  contains  the  chlorophyll  and  hence  is  stained  green. 
The  chlorophyll-containing  plastid  is  known  as  the  cliloro- 
flastid,  or  chloroplast  (Fig.  1).  An  ordinary  alga-cell,  there- 
fore, consists  of  a  cell  wall,  within  which  the  protoplasm  is 
organized  into  cytoplasm,  nucleus,  and  chloroplasts. 

The  bodies  of  the  simplest  Algge  consist  of  one  such 
cell,  and  it  may  be  regarded  as  the  simplest  form  of  plant 
body.  Starting  with  such  forms,  one  direction  of  advance 
in  complexity  is  to  organize  several  such  cells  into  a  loose 
row,  which  resembles  a  chain  (Fig.  4) ;  in  other  forms  the 
cells  in  a  row  become  more  compacted  and  flattened,  form- 
ing a  simple  filament  (Figs.  2,  5) ;  in  still  other  forms  the 
original  filament  puts  out  branches  like  itself,  producing 
a  branching  filament  (Fig.  8).  These  filamentous  bodies 
are  very  characteristic  of  the  Algae. 

Starting  again  with  the  one-celled  body,  another  line  of 
advance  is  for  several  cells  to  organize  in  two  directions, 
forming  a  plate  of  cells.  Still  another  line  of  advance  is  for 
the  cells  to  organize  in  three  directions,  forming  a  mass  of 
cells. 

The  bodies  of  Algae,  therefore,  may  be  said  to  be  one- 
celled  in  the  simplest  forms,  and  in  the  most  complex  forms 
they  become  filaments,  plates,  or  masses  of  cells. 

11.  Reproduction. — In  addition  to  the  work  of  nutrition, 
the  plant  body  must  organize  for  reproduction.  Just  as  the 
nutritive  body  begins  in  the  lowest  forms  with  a  single  cell 


TIIALLOPIIYTES:    ALG^  9 

and  becomes  more  complex  in  the  higher  forms,  so  repro- 
duction begins  in  very  simple  fashion  and  gradnally  be- 
comes more  comjjlex.  Two  general  types  of  reproduction 
are  employed  by  the  Algae,  and  all  other  plants.  They  are 
as  follows : 

(1)  Vegetative  multiplication. — This  is  the  only  type  of 
reproduction  employed  by  the  lowest  Algas,  but  it  persists 
in  all  higher  groups  even  when  the  other  method  has  been 
introduced.  In  this  type  no  special  reproductive  bodies  are 
formed,  but  the  ordinary  vegetative  body  is  used  for  the 
purpose.  For  example,  if  the  body  consists  of  one  cell,  that 
cell  cuts  itself  into  two,  each  half  grows  and  rounds  off  as 
a  distinct  cell,  and  two  new  bodies  appear  where  there  was 
one  before  (Figs.  3,  6).  This  process  of  cell  division  is  very 
complicated  and  important,  involving  a  division  of  nucleus 
and  cytoplasm  so  that  the  new  cells  may  be  organized  just 
as  was  the  old  one.  Wherever  ordinary  nutritive  cells  are 
used  directly  to  produce  new  plant  bodies  the  process  is 
vegetative  vudtiplication.  This  method  of  rejiroduction  may 
be  indicated  by  a  formula  as  follows  :  P  —  P  —  P  —  P  —  P,  in 
which  P  stands  for  the  plant,  the  formula  indicating  that 
a  succession  of  plants  may  arise-  directly  from  one  another 
without  the  interposition  of  any  special  structure. 

(2)  Spores. — Spores  are  cells  which  are  specially  organ- 
ized to  reproduce,  and  are  not  at  all  concerned  in  the  nutri- 
tive work  of  the  plant.  Spores  are  all  alike  in  their  power 
of  reproduction,  but  they  are  formed  in  two  very  distinct 
ways.  It  must  be  remembered  that  these  two  tyj^es  of 
spores  are  alike  in  power  but  different  in  origin. 

Asexual  spores. — These  cells  are  formed  by  cell  divi- 
sion. A  cell  of  the  plant  body  is  selected  for  the  purpose, 
and  usually  its  contents  divide  and  form  a  variable  number 
of  new  cells  within  the  old  one  (Fig.  2,  B).  These  new  cells 
are  asexual  spores.,  and  the  cell  which  has  formed  them 
within  itself  is  known  as  tlie  mother  cell.  This  peculiar 
kind  of  cell  division,  which  does  not  involve  the  wall  of  the 


IQ  PLANT   STKUCTUKES 

old  cell,  is  often  called  internal  division,  to  distinguish  it 
from  fission,  which  involves  the  wall  of  the  old  cell,  and  is 
the  ordinary  method  of  cell  division  in  nutritive  cells. 

If  the  mother  cell  which  produces  the  spores  is  different 
from  the  other  cells  of  the  plant  body  it  is  called  the  sporan- 
giu7n,  which  means  "  spore  vessel."  Often  a  cell  is  nutri- 
tive for  a  time  and  afterward  becomes  a  mother  cell,  m 
which  case  it  is  said  to  function  as  a  sporangium.  The  wall 
of  a  sporangium  usually  opens,  and  the  spores  are  dis- 
charged, thus  being  free  to  produce  new  plants.  Various 
names  have  been  given  to  asexual  spores  to  indicate  certain 
peculiarities.  As  Algas  are  mostly  surrounded  by  water, 
the  characteristic  asexual  spore  in  the  group  is  one  that 
can  swim  by  means  of  minute  hair-like  processes  or  cilia, 
which  have  the  power  of  lashing  the  water  (Fig.  7,  C). 
These  ciliated  spores  are  known  as  zoospores,  or  "  animal- 
like spores,"  referring  to  their  power  of  locomotion ;  some- 
times they  are  called  sjcimming  spares,  or  swarm  spores.  It 
must  be  remembered  that  all  of  these  terms  refer  to  the 
same  thing,  a  swimming  asexual  spore. 

This  method  of  reproduction  may  be  indicated  by  a  for- 
mula as  follows  :  P  —  o  —  P  —  o  —  P  —  o  —  P,  which  indi- 
cates that  new  plants  are  not  produced  directly  from  the 
old  ones,  as  in  vegetative  multiplication,  but  that  between 
the  successive  generations  there  is  the  asexual  spore. 

Sexual  spores. — These  cells  are  formed  by  cell  union, 
two  cells  fusing  together  to  form  the  spore.  This  process 
of  forming  a  spore  by  the  fusion  of  two  cells  is  called  the 
sexual  process,  and  the  two  special  cells  (sexual  cells)  thus 
used  are  known  as  gametes  (Fig.  2,  C,  d,  e).  It  must  be 
noticed  that  gametes  are  not  spores,  for  they  are  not  able 
alone  to  produce  a  new  plant ;  it  is  only  after  two  of  them 
have  fused  and  formed  a  new  cell,  the  spore,  that  a  plant 
can  be  produced.  The  spore  thus  formed  does  not  differ 
in  its  power  from  the  asexual  spore,  but  it  differs  very 
much  in  its  method  of  origin. 


TIIALLOPIIYTES:   ALG^  H 

The  gametes  are  organized  within  a  mother  cell,  and  if 
this  cell  is  distinct  from  the  other  cells  of  the  plant  it  is 
called  a  gametanginm,  which  means  "  gamete  vessel." 

This  method  of  reproduction  may  be  indicated  by  a  for- 
mula as  follows  :  P  =  °>o  —  P  =  °>o  —  P  =  ^>o  —  P, 
which  indicates  that  two  special  cells  (gametes)  are  pro- 
duced by  the  plant,  that  these  two  fuse  to  form  one  (sexual 
spore),  which  then  produces  a  new  plant. 

It  must  not  be  supposed  that  if  a  plant  uses  one  of  these 
three  methods  of  reproduction  (vegetative  multiplication, 
asexual  spores,  sexual  spores)  it  does  not  employ  the  other 
two.  All  three  methods  may  be  employed  by  the  same 
plant,  so  that  new  plants  may  arise  from  it  in  three  differ- 
ent#v7ays. 


CHAPTEK   III 

THE  EVOLUTION  OF  SEX 

12.  The  general  problem. — In  the  last  chapter  it  was  re- 
marked that  the  simplest  Algae  reproduce  only  by  vegetative 
multiplication,  the  ordinary  cell  division  (fission)  of  nutri- 
tive cells  multiplying  cells  and  hence  individuals.  Among 
other  low  Algfe  asexual  spores  are  added  to  fission  as  a 
method  of  reproduction,  the  spores  being  also  formed  by 
cell  division,  generally  internal  division.  In  higher  forms 
gametes  appear,  and  a  new  method  of  reproduction,  the 
sexual,  is  added  to  the  other  two. 

Sexual  reproduction  is  so  important  a  process  in  all 
plants  except  the  lowest,  that  it  is  of  interest  to  discover 
how  it  may  have  originated,  and  how  it  developed  into  its 
highest  form.  Among  the  Algae  the  origin  and  develop- 
ment of  the  sexual  process  seems  to  be  plainly  suggested  ; 
and  as  all  other  plant  groups  have  probably  been  derived 
more  or  less  directly  from  Algae,  what  has  been  accom- 
plished for  the  sexual  process  in  this  lowest  group  was 
probably  done  for  the  whole  plant  kingdom. 

13.  The  origin  of  gametes. — One  of  the  best  Algae  to 
illustrate  the  possible  origin  of  gametes  is  a  common  fresh- 
water form  known  as  Ulothrix  (Fig.  2).  The  body  consists 
of  a  simple  filament  composed  of  a  single  row  of  short 
cells  (Fig.  2,  A).  Each  cell  contains  a  nucleus,  and  a 
single  large  chloroplast  which  has  the  form  of  a  thick  cyl- 
inder investing  the  rest  of  the  cell  contents.  Through  the 
microscope,  if  the  focus  is  upon  the  center  of  the  cell, 
an  optical  section  of  the  cylinder  is  obtained,  the  chloro- 

13 


THE   EVOLUTION   OF  SEX 


13 


plast  appearing  as  a  thick  green  mass  on  each  side  of  the 
central  nucleus.  As  no  other  color  appears,  it  is  evident 
that  Ulothrix  is  one  of  the  Chlorophyceas. 


Fig.  2.  Ulothrix,  a  Conferva  form.  A,  base  of  filament,  showing  lowest  holdfast 
cell  and  five  vegetative  cells,  each  with  its  single  conspicuous  cylindrical  chloro- 
plast  (seen  in  section)  inclosing  a  nucleus;  B,  four  cells  containing  numerous 
small  zoospores,  the  others  emptied;  f,  fragment  of  a  filament  showing  one  cell 
(a)  containing  four  zoospores,  another  zoospore  {b)  displaying  four  cilia  at  its 
pointed  end  and  just  having  escaped  from  its  cell,  another  cell  (c)  from  which 
most  of  the  small  biciliate  gametes  have  escaped,  gametes  pairing  (d"),  and  the 
resulting  zygotes  (<?)  ;  D,  beginning  of  new  filament  from  zoospore  ;  E,  feeble 
filaments  formed  by  the  small  zoospores  ;  F,  zygote  growing  after  rest;  G, 
zoospores  produced  by  zygote.— Caldwell,  except  F  and   G,  which  are  after 

DODEL-PORT. 


The  cells  are  all  alike,  excepting  that  the  lowest  one  of 
the  filament  is  mostly  colorless,  and  is  elongated  and  more 
or  less  modified  to  act  as  a  holdfast,  anchoring  the  filament 
to  some  firm  support.  With  this  exception  the  cells  are  all 
nutritive  ;  hut  any  one  of  them  has  the  power  of  organizing 
for  reproduction.     This  indicates  that  at  first  nutritive  and 


14:  PLANT   STKUCTURES 

reproductive  cells  are  not  distinctly  differentiated,  but  that 
the  same  cell  may  be  nutritive  at  one  time  and  reproductive 
at  another. 

In  suitable  conditions  certain  cells  of  the  filament  will 
be  observed  organizing  within  themselves  new  cells  by 
internal  division  (Fig.  2,  C,  «,  h).  The  method  of  forma- 
tion at  once  suggests  that  the  new  cells  are  asexual  spores, 
and  the  mother  cell  which  produces  them  is  acting  as  a 
sporangium.  The  spores  escape  into  the  water  through  an 
opening  formed  in  the  wall  of  the  mother  cell,  and  each  is 
observed  to  have  four  cilia  at  the  pointed  end,  by  means  of 
which  it  swims,  and  hence  it  is  a  zoospore  or  swarm  spore. 
After  swimming  about  for  a  time,  the  zoospores  "  settle 
down,"  lose  their  cilia,  and  begin  to  develop  a  new  filament 
like  that  from  which  they  came  (Fig.  2,  D). 

Other  cells  of  the  same  filament  also  act  as  mother  cells, 
but  the  cells  which  they  produce  are  more  numerous,  hence 
smaller  in  size  than  the  zoospores,  and  they  have  but  two 
cilia  (Fig.  2,  (7,  c).  They  also  escape  into  the  water  and 
swim  about,  except  in  size  and  in  number  of  cilia  resem- 
bling the  zoospores.  In  general  they  seem  to  be  unable  to 
act  as  the  zoospores  in  the  formation  of  new  filaments,  but 
occasionally  one  of  them  forms  a  filament  much  smaller 
than  the  ordinary  one  (Fig.  2,  E).  This  indicates  that 
they  may  be  zoospores  reduced  in  size,  and  unable  to  act  as 
the  larger  ones.  The  important  fact,  however,  is  that 
these  smaller  swimming  cells  come  together  in  pairs,  each 
pair  fusing  into  one  cell  (Fig.  2,  C\  d,  e).  The  cells  thus 
formed  have  the  power  of  producing  new  filaments  more  or 
less  directly. 

It  is  evident  that  this  is  a  sexual  act,  that  the  cell  pro- 
duced by  fusion  is  a  sexual  spore,  that  the  two  cells  which 
fuse  are  gametes,  and  that  the  mother  cell  which  produces 
them  acts  as  a  gametangium.  Cases  of  this  kind  suggest 
that  the  gametes  or  sex  cells  have  been  derived  from  zoo- 
spores, and  that  asexual  spores  have  given  rise  to  sex  cells. 


THE   EVOLUTION   OF   SEX  15 

The  appearance  of  sex  cells  (gametes)  is  but  one  step  in  the 
evolution  of  sex.  It  represents  the  attainment  of  sexuality, 
but  the  process  becomes  much  more  highly  developed. 

14.  Isogamy. — When  gametes  first  appear,  in  some  such 
way  as  has  been  described,  the  two  which  fuse  seem  to  be 
exactly  alike.  They  resemble  each  other  in  size  and  activ- 
ity, and  in  every  structure  which  can  be  distinguished. 
This  fact  is  indicated  by  the  word  isogamy,  which  means 
"  similar  gametes,"  and  those  plants  whose  pairing  gametes 
are  similar,  as  Ulothrix,  are  said  to  be  isogamous. 

The  act  of  fusing  of  similar  gametes  is  usually  called 
conjugation^  which  means  a  "  yoking  together  "  of  similar 
bodies.  Of  course  it  is  a  sexual  process,  but  the  name  is 
convenient  as  indicating  not  merely  the  process,  but  also  an 
important  character  of  the  gametes.  The  sexual  spore 
which  results  from  this  act  of  conjugation  is  called  the 
zygote  or  zygospore,  meaning  "  yoked  spore." 

In  isogamy  it  is  evident  that  while  sexuality  has  been 
attained  there  is  no  distinction  between  sexes,  as  obtains  in 
the  higher  plants.  It  may  be  called  a  unisexual  condition, 
as  opposed  to  a  bisexual  one.  The  next  problem  in  the 
evolution  of  sex,  therefore,  is  to  discover  how  a  bisexual 
condition  has  been  derived  from  a  unisexual  or  isogamous 
one. 

15.  Heterogamy. — Beginning  with  isogamous  forms,  a 
series  of  plants  can  be  selected  illustrating  how  the  pairing 
gametes  gradually  became  unlike.  One  of  them  becomes 
less  active  and  larger,  until  finally  it  is  entirely  passive  and 
very  many  times  larger  than  its  mate  (Fig.  7).  The  other 
retains  its  small  size  and  increases  in  activity.  The  pairing 
gametes  thus  become  very  much  differentiated,  the  larger 
passive  one  being  the  female  gamete,  the  smaller  active  one 
the  male  gamete.  This  condition  is  indicated  by  the  word 
heterogamy,  which  means  "  dissimilar  gametes,"  and  those 
plants  whose  pairing  gametes  are  dissimilar  are  said  to  be 
heterogamous. 


16  PLANT   STEUCTUKES 

In  order  to  distinguish  them  the  large  and  passive  female 
gamete  is  called  the  oosphere,  which  means  "  egg  sphere," 
or  it  is  called  the  egg  ;  the  small  but  active  male  gamete  is 
variously  called  the  s23ermatozoid,  the  anther ozoid^  or  simply 
the  sperm.  In  this  book  egg  and  sperm  will  be  used,  the 
names  of  similar  structures  in  animals. 

In  isogamous  plants  the  mother  cells  (gametangia) 
which  produce  the  gametes  are  alike ;  but  in  heterogamous 
plants  the  gametes  are  so  unlike  that  the  gametangia  which 
produce  them  become  unlike.  Accordingly  they  have  re- 
ceived distinctive  names,  the  gametangium  which  produces 
the  sperms  being  called  the  antheridium,  that  producing  the 
egg  being  called  the  oogonium  (Fig.  10). 

The  act  of  fusing  of  sperm  and  egg  is  called  fertiliza- 
tion, which  is  the  common  form  of  the  sexual  process.  The 
sexual  spore  which  results  from  fertilization  is  known  as  the 
oospore  or  "  egg-spore,"  sometimes  called  the  fertilized  egg. 

It  is  evident  that  heterogamous  plants  are  bisexual,  and 
bisexuality  is  not  only  attained  among  Algffi,  but  it  prevails 
among  all  higher  plants.  Among  the  lowest  forms  there  is 
only  vegetative  multiplication  ;  higher  forms  added  sexu- 
ality ;  then  still  higher  forms  became  bisexual. 

16.  Simmiary. — Isogamous  forms  produce  gametangia, 
which  produce  similar  gametes,  which  by  conjugation  form 
zygotes.  Heterogamous  forms  produce  antheridia  and 
oogonia,  which  produce  sperms  and  eggs,  which  by  fertiliza- 
tion form  oospores. 


CHAPTEE  IV 

THE  GREAT  GROUPS  OF  ALG^ 

17.  General  characters. — The  Algae  are  distinguished 
among  ThalloiDliytes  by  the  presence  of  chlorophyll.  It 
was  stated  in  a  previous  chapter  that  in  three  of  the  four 
great  groups  another  coloring  matter  is  associated  with  the 
chlorophyll,  and  that  this  fact  is  made  the  basis  of  a  division 
into  Blue-green  Algse  (Cyanophycese),  Green  AlgEe  (Chloro- 
phyceae),  Brown  Algae  (PhajophyccEe),  and  Eed  Algee  (Rhodo- 
phyceae).  In  our  limited  space  it  will  be  impossible  to  do 
more  than  mention  a  few  representatives  of  each  group, 
but  they  will  serve  to  illustrate  the  prominent  facts. 

1.  Cyanophtce^  {Blue-green  Algce) 

18.  Gloeocapsa. — These  forms  may  be  found  forming 
blue-green  or  olive-green  patches  on  damp  tree-trunks,  rock, 
walls,  etc.  By  means  of  the  microscope  these  patches  are 
seen  to  be  composed  of  multitudes  of  spherical  cells,  each 
representing  a  complete  Gloeocapsa  body.  One  of  the  pecul- 
iarities of  the  body  is  that  the  cell  wall  becomes  mucilagi- 
nous, swells,  and  forms  a  Jelly-like  matrix  about  the  work- 
ing cell.  Each  cell  divides  in  the  ordinary  way,  two  new 
Gloeocapsa  individuals  being  formed,  this  method  of  vegeta- 
tive multiplication  being  the  only  form  of  reproduction 
(Fig.  3). 

When  new  cells  are  formed  in  this  way  the  swollen 
mucilaginous  walls  are  apt  to  hold  them  together,  so  that 
presently  a  number  of  cells  or  individuals  are  found  lying 

17 


18 


PLANT   STRUCTURES 


together  imbedded  in  the  Jelly-like  matrix  formed  by  the 
wall  material  (Fig.  3).  These  imbedded  groups  of  individ- 
uals are  spoken  of  as  colonies,  and  as 
colonies  become  large  they  break  up 
into  new  colonies,  the  individual  cells 
composing  them  continuing  to  divide 
and  form  nevf  individuals.  This  rep- 
resents a  very  simple  life  liistory,  in 
fact  a  siqjpler  one  could  hardly  be 
imagined. 

19.  Nostoc. — These  forms  occur  in 
jelly-like  masses  in  damp  places.  If 
the  jelly  be  examined  it  will  be  found 
to  contain  imbedded  in  it  numerous 
cells  like  those  of  Glmocapui,  but  they 
are  strung  together  to  form  chains  of 
varying  lengths  (Fig.  4).  The  Jelly  in 
which  these  chains  are  imbedded  is  the 
same  as  that  found  in  Gloeocapsa,  being 
formed  by  the  cell  walls  becoming  mucilaginous  and  swollen. 
One  notable  fact  is  that  all  the  cells  in  the  chain  are  not 
alike,  for  at  irregu- 
lar intervals  there  oc- 
cur larger  colorless 
cells,  an  illustration 
of  the  differentiation 
of  cells.  These  larger 
cells  are  known  as  het- 
erocysts  (Fig.  4,  A), 
which  simply  means 
"  other  cells."  It  is 
observed  that  when 
the  chain  breaks  up 

into    fragments    each        Pig.   4.     Nostoc,  a  blue-green  alga,  showing  the 

fragment  is  composed  chain-like   filaments    and    the    heterocysts   (^) 

"  ■'^  which  determine  the  breaking  up  of  the  chain. 

of  the  cells  between         -caldwell. 


Fig.  3.  Gkeocapsa,  a  blue- 
green  alga,  showing 
single  cells,  and  small 
groups  which  have  been 
formed  by  division  and 
are  held  together  by  the 
enveloping  mucilage. — 
Caldwell. 


THE   GREAT   GROUPS   OF   ALG^ 


19 


two  heterocysts.  The  fragments  wriggle  out  of  the  jelly 
matrix  and  start  new  colonies  of  chains,  each  cell  dividing 
to  increase  the  length  of  the  chain.  This  cell  division, 
to  form  new  cells,  is  the  characteristic  method  of  repro- 
duction. 

At  the  approach  of  unfavorable  conditions  certain  cells 
of  the  chain  become  thick-walled  and  well-protected.  These 
cells  which  endure  the  cold  or  other  hardships,  and  upon 
the  return  of  favorable  conditions  produce  new  chains  of 
cells,  are  often  called  spores,  but  they  are  better  called 
"  resting  cells." 

20.  Oscillatoria. — These  forms  are  found  as  bluish-green 
slippery  masses  on  wet  rocks,  or  on  damp  soil,  or  freely 
floating.  They  are  simple  filaments,  composed  of  very  short 
flattened  cells  (Fig.  5),  and  the  name 
Oscillatoria  refers  to  the  fact  that  they 
exhibit  a  peculiar  oscillating  move- 
ment. These  motile  filaments  are  iso- 
lated, not  being  held  together  in  a 
jelly-like  matrix  as  are  the  chains  of 
Nostoc^  but  the  wall  develops  a  cer- 
tain amount  of  mucilage,  which  gives 
the  slippery  feeling  and  sometimes 
forms  a  thin  mucilaginous  sheath 
about  the  row  of  cells. 

The  cells  of  a  filament  are  all  alike, 
except  that  the  terminal  cell  has  its 
free  surface  rounded.  If  a  filament 
breaks  and  a  new  cell  surface  ex- 
posed, it  at  once  becomes  rounded. 
If  a  single  cell  of  the  filament  is 
freed  from  all  the  rest,  both  flattened  ends  become  rounded, 
and  the  cell  becomes  spherical  or  nearly  so.  These  facts 
indicate  at  least  two  important  things  :  (1)  that  the  cell 
wall  is  elastic,  so  that  it  can  be  made  to  change  its  form, 
and  (2)  that  it  is  pressed  upon  from  within,  so  that  if  free 


<(^ 


~ 


•^\ 


B 


Fio.  5.  Oscillatoria,  a 
blue-green  alga,  show- 
ing a  group  of  filaments 
(A),  and  a  single  fila- 
ment more  enlarged  (B). 
—Caldwell. 


20  PLANT  STRUCT  CJEES 

it  will  bulge  outward.     In  all  active  living  cells  there  is 
this  pressure  upon  the  wall  from  within. 

Each  cell  of  the  Oscillator' ia  filament  has  the  power  of 
dividing,  thus  forming  new  cells  and  elongating  the  fila- 
ment. A  filament  may  break  up  into  fragments  of  varying 
lengths,  and  each  fragment  by  cell  division  organizes  a  new 
filament.  Here  again  reproduction  is  by  means  of  vegeta- 
tive multiplication. 

21.  Conclusions.— Taking  Glmocapsa,  Nostoc,  and  Oscil- 
latoria  as  representatives  of  the  group  Cyanophycese,  or 
"  green  slimes,"  we  may  come  to  some  conclusions  concern- 
ing the  group  in  general.  The  plant  body  is  very  simple, 
consisting  of  single  cells,  or  chains  and  filaments  of  cells. 
Although  in  Nostoc  and  Oscillatoria  the  cells  are  organized 
into  chains  and  filaments,  each  cell  seems  to  be  able  to  live 
and  act  independently,  and  the  chain  and  filament  seem  to 
be  little  more  than  colonies  of  individual  cells.  In  this 
sense,  all  of  these  plants  may  be  regarded  as  one-celled. 

Differentiation  is  exhibited  in  the  appearance  of  hetero- 
cysts  in  Nostoc,  peculiar  cells  which  seem  to  be  connected 
in  some  way  with  the  breaking  up  of  filamentous  colonies, 
although  the  Oscillatoria  filament  breaks  up  without  them. 

The  power  of  motion  is  also  well  exhibited  by  the  group, 
the  free  filaments  of  Oscillatoria  moving  almost  continu- 
ally, and  the  imbedded  chains  of  Nostoc  at  times  moving  to 
escape  from  the  restraining  mucilage. 

The  whole  group  also  shows  a  strong  tendency  in  the 
cell-wall  material  to  become  converted  into  mucilage  and 
much  swollen,  a  tendency  which  reaches  an  extreme  expres- 
sion in  such  forms  as  Nostoc  and  Glmocapsa. 

Another  distinguishing  mark  is  that  reproduction  is 
exclusively  by  means  of  vegetative  multiplication,  through 
ordinary  cell  division  or  fission,  which  takes  place  very 
freely.  Individual  cells  are  organized  with  heavy  resistant 
walls  to  enable  them  to  endure  the  winter  or  other  unfavor- 
able conditions,  and  to  start  a  new  series  of  individuals 


THE   GREAT   GEOUPS   OF  ALG^ 


21 


upon  the  return  of  favorable  conditions.  These  may  be 
regarded  as  resting  cells.  So  notable  is  the  fact  of  repro- 
duction by  fission  that  Cyanophycege  are  often  separated 
from  the  other  groups  of  Algae  and  spoken  of  as  "  Fission 
Algffi,"  which  put  in  technical  form  becomes  Schizophyceae. 
In  this  particular,  and  in  several  others  mentioned  above, 
they  resemble  the  "  Fission  Fungi "  (Schizomycetes),  com- 
monly called  "bacteria,"  so  closely  that  they  are  often 
associated  with  them  in  a  common  group  called  "Fis- 
sion plants"  (Schizophytes),  distinct  from  the  ordinary 
Algse  and  Fungi. 


2.  Chlorophtce^  (Green  Algce). 


22.  Pleurococcus.- 

celled  Green  Algae, 
covering  damp  tree 
stain.  These  fine- 
ly granular  green 
masses  are  found 
to  be  made  up 
of  multitudes  of 
spherical  cells  re- 
sembling those  of 
Gloeocapsn,  except 
that  there  is  no 
blue  with  the  chlo- 
rophyll, and  the 
cells  are  not  im- 
bedded in  such 
jelly-like  masses. 
The  cells  may  be 
solitary,  or  may 
cling  together  in 
colonies  of  various 
divides  and  forms 
20 


-This  may  be  taken  as  a  type  of  one- 
It  is  most  commonly  found  in  masses 
■trunks,  etc.,  and  looking  like  a  green 


Fig.  6.  Pleurococcus,  a  one-celled  green  alga  :  A,  show- 
ing the  adult  form  with  its  nucleus  ;  B.  C,  D,  E, 
various  stages  of  division  (fission)  in  producing  new 
cells  ;  F,  colonies  of  cells  which  have  remained  in 
contact. — C  aldwell. 


sizes  (Fig.  6).     Like  Glceocapsa,  a  cell 
two  new  cells,  the   only  reproduction 


22  PLANT   STRUCTURES 

being  of  this  simple  kind.  It  is  evident,  therefore,  that  the 
group  Chlorophyceae  begins  with  forms  just  as  simple  as 
are  to  be  found  among  the  Cyanophycea?. 

Pleurococcus  is  used  to  represent  the  group  of  Protococ- 
cus  forms,  one-celled  forms  which  constitute  one  of  the 
subdivisions  of  the  Green  Algfe.  It  should  be  said  that 
Pleurococcus  is  possibly  not  a  Protococcus  form,  but  may 
be  a  reduced  member  of  some  higher  group ;  but  it  is  so 
common,  and  represents  so  well  a  typical  one-celled  green 
alga,  that  it  is  used  in  this  connection.  It  should  be 
known,  also,  that  while  the  simplest  Protococcus  forms  re- 
produce only  by  fission,  others  add  to  this  the  other  meth- 
ods of  reproduction. 

23.  XJlothrix. — This  form  was  described  in  §  13.  It 
is  very  common  in  fresh  waters,  being  recognized  easily  by 
its  simple  filaments  composed  of  short  squarish  cells,  each 
cell  containing  a  single  conspicuous  cylindrical  chloroplast 
(Fig.  2).  This  plant  uses  cell  division  to  multiply  the  cells 
of  a  filament,  and  to  develop  new  filaments  from  fragments 
of  old  ones ;  but  it  also  produces  asexual  spores  in  the  form 
of  zoospores,  and  gametes  which  conjugate  and  form  zygotes. 
Both  zoospores  and  zygotes  have  the  power  of  germination — 
that  is,  the  power  to  begin  the  development  of  a  new  plant. 
In  the  germination  of  the  zygote  a  new  filament  is  not  pro- 
duced directly,  but  there  are  formed  within  it  zoospores, 
each  of  which  produces  a  new  filament  (Fig.  2,  F,  G).  All 
three  kinds  of  reproduction  are  represented,  therefore,  but 
the  sexual  method  is  the  low  type  called  isogamy,  the  pair- 
ing gametes  being  alike. 

Ulothrix  is  taken  as  a  representative  of  the  Conferva 
forms,  the  most  characteristic  group  of  Chlorophyceae. 
All  the  Conferva  forms,  however,  are  not  isogamous,  as  will 
be  illustrated  by  the  next  example. 

24.  (Edogonium. — This  is  a  very  common  green  alga, 
found  in  fresh  waters  (Fig.  7).  The  filaments  are  long  and 
simple,  the  lowest  cell  acting  as  a  holdfast,  as  in  Ulothrix 


Fig.  7.  (Edogonium  nodosum,  a  Conferva  form  :  A,  portion  of  a  filament  showing  a 
vecetativc  cell  with  its  nucleus  id),  an  oogonium  (a)  filled  by  an  egg  packed  with 
food  material,  a  second  oogonium  (c)  containing  a  fertilized  egg  or  oospore  as 
shown  by  the  heavy  wall,  and  two  antheridia  (b),  each  containing  two  sperms;  B, 
another  filament  showing  antheridia  (a)  from  which  two  sperms  (b)  have  escaped, 
a  vegetative  cell  with  its  nucleus,  and  an  oogonium  which  a  sperm  (c)  has  entered 
and  is  coming  in  contact  with  the  egg  whose  nucleus  id)  may  be  seen;  C,  a  zoo- 
spore which  has  been  formed  in  a  vegetative  cell,  showing  the  crown  of  cilia  and 
the  clear  apex,  as  in  the  sperms;  I),  a  zoospore  producing  a  now  filament,  putting 
out  a  holdfast  at  base  and  elongating;  E,  a  further  stage  of  development;  F,  the 
four  zoospores  formed  by  the  oospore  when  it  germinates.— Caldwell,  except 
C  and  F,  which  are  after  Pringsheim. 


24  PLANT   STRUCTURES 

(§  13).  The  other  cells  are  longer  than  in  Ulothrix,  each 
cell  containing  a  single  nuclens  and  apparently  several 
chloroplasts,  hut  really  there  is  but  one  large  complex 
chloroplast. 

The  cells  of  the  filament  have  the  power  of  division, 
thus  increasing  the  length  of  the  filament.  Any  cell  also 
may  act  as  a  sporangium,  the  contents  of  a  mother  cell  ^ 
organizing  a  single  large  asexual  spore,  which  is  a  zoospore,  f 
The  zoospore  escapes  from  the  mother  cell  into  the  water, 
and  at  its  more  pointed  clear  end  there  is  a  little  crown  of 
cilia,  by  means  of  which  it  swims  about  rapidly  (Fig.  7,  C). 
After  moving  about  for  a  time  the  zoospore  comes  to  rest, 
attaches  itself  by  its  clear  end  to  some  support,  elongates, 
begins  to  divide,  and  develops  a  new  filament  (Fig.  7,  D,  E). 
Other  cells  of  the  filament  become  very  different  from 
the  ordinary  cells,  swelling  out  into  globular  form  (Fig.  7, 
A,  B),  and  each  such  cell  organizes  within  itself  a  single 
large  egg  (oosphere).  As  the  egg  is  a  female  gamete,  the 
large  globvilar  cell  which  produces  it,  and  which  is  differen- 
tiated from  the  other  cells  of  the  body,  is  the  oogonium. 
A  perforation  in  the  oogonium  wall  is  formed  for  the 
entrance  of  sperms. 

Other  cells  in  the  same  filament,  or  in  some  other  fila- 
ment, are  observed  to  differ  from  the  ordinary  cells  in 
being  much  shorter,  as  though  an  ordinary  cell  had  been 
divided  several  times  without  subsequent  elongation  (Fig. 
7,  A,  f,  B,  a).  In  each  of  these  short  cells  one  or  two 
sperms  are  organized,  and  therefore  each  short  cell  is  an 
antheridium.  When  the  sperms  are  set  free  they  are  seen 
to  resemble  very  small  zoospores,  having  the  same  little 
crown  of  cilia  at  one  end. 

The  sperms  swim  actively  about  in  the  vicinity  of  the 
oogonia,  and  sooner  or  later  one  enters  the  oogonium 
through  the  perforation  provided  in  the  wall,  and  fuses 
with  the  egg  (Fig.  7,  B,  c).  As  a  result  of  this  act  of  fer- 
tilization an  oospore  is  formed,  which  organizes  a  firm  wall 


THE   GREAT   GROUPS   OF  ALG^ 


25 


about  itself.  This  firm  wall  indicates  that  the  oospore  is 
not  to  germinate  immediately,  but  is  to  pass  into  a  resting 
condition.  Spores  which  form  heavy  walls  and  pass  into 
the  resting  con- 
dition are  often 
spoken  of  as  "  rest- 
ing spores,"  and  it 
is  very  common 
for  the  zygotes 
and  oospores  to 
be  resting  spores. 
These  resting 
spores  enable  the 
plant  to  endure 
through  unfavor- 
able conditions, 
such  as  failure  of 
food  supply,  cold, 
drought,  etc. 
When  favorable 
conditions  return, 
the  protected  rest- 
ing spore  is  ready 
for  germination. 

When  the 
oospore  of  (Edogo- 
niiirn   germinates 

it  does  not  develop  directly  into  a  new  filament,  but  the 
contents  become  organized  into  four  zoospores  (Fig.  7,  F)y 
which  escape,  and  each  zoospore  develops  a  filament.  In 
this  way  each  oospore  may  give  rise  to  four  filaments. 

It  is  evident  that  (Edogonium  is  a  heterogamous  plant, 
and  is  another  one  of  the  Conferva  forms.  Conferva  bodies 
are  not  always  simple  filaments,  as  are  those  of  Ulothrix 
and  Wdogonium^  but  they  are  sometimes  extensively  branch- 
ing filaments,  as  in  Cladophora,  a  green  alga  very  common 


Fig.  8.  Cladophora,  a  branching  green  alga,  a  very 
small  part  of  the  plant  being  shown.  The  branches 
arise  at  the  upper  ends  of  cells,  and  the  cells  are 
ccenocy  tic.  —Caldwell. 


26 


PLANT   STEUCTUKES 


in  rivers  and  lakes  (Fig.  8).  The  cells  are  long  and  densely 
crowded  with  chloroplasts  ;  and  in  certain  cells  at  the  tips 
of  branches  large  numbers  of  zoospores  are  formed,  which 
have  two  cilia  at  the  pointed  end,  and  hence  are  said  to  be 
hiciliate. 

25.  Vaucheria. — This  is  one  of  the  most  common  of  the 
Green  Algse,  found  in  felt-like  masses  of  coarse  filaments  in 
shallow  water  and  on  muddy  banks,  and  often  called  "  green 


Fig.  9.  Vavcheria  geminata,  a  Siphon  form,  showing  a  portion  of  the  coenocytic 
body  (A)  which  has  sent  out  a  branch  at  the  tip  of  which  a  sporangium  (B) 
formed,  within  which  a  large  zoospore  was  organized,  and  from  which  (D)  it  is 
discharged  later  as  a  large  multiciliate  body  (f ),  which  then  begins  the  develop- 
ment of  a  new  ccenocytic  body  (J?).— Caldwell. 


felt."  The  filament  is  very  long,  and  usually  branches  ex- 
,  tensively,  but  its  great  peculiarity  is  that  there  is  no  parti- 
tion wall  in  the  whole  body,  which  forms  one  long  continuous 
cavity  (Figs.  9,  11).  This  is  sometimes  spoken  of  as  a  one- 
celled  body,  but  it  is  a  mistake.  Imbedded  in  the  exten- 
sive cytoplasm  mass,  which  fills  the  whole  cavity,  there  are 
not  only  very  numerous  chloroplasts,  but  also  numerous 
nuclei.     As  has  been  said,  a  single  nucleus  with  some  cyto- 


THE   GREAT   GROUPS   OF   ALG^  27 

plasm  organized  about  it  is  a  cell,  whether  it  has  a  wall  or 
not.  Therefore  the  body  of  Vauclieria  is  made  up  of  as 
many  cells  as  there  are  nuclei,  cells  whose  protoplasmic 
structures  have  not  been  kept  separate  by  cell  wills.  Such 
a  body,  made  up  of  numerous  cells,  but  with  no  partitions, 
is  called  a  cmiocijte,  or  it  is  said  to  be  cmiocytic.  Vauclieria 
represents  a  great  group  of  Chlorophycese  whose  members 
have  coenocytic  bodies,  and  on  this  account  they  are  called 
the  Siphon  forms, 

Vauclieria  produces  very  large  zoospores.  The  tip  of  a 
branch  becomes  separated  from  the  rest  of  the  body  by  a 
partition  and  thus  acts  as  a  sporangium  (Fig.  9,  B).  In 
this  improvised  sporangium  the  whole  of  the  contents  or- 
ganize a  single  large  zoospore,  which  is  ciliated  all  over, 
escapes  by  squeezing  through  a  perforation  in  the  wall 
(Fig.  9,  6'),  swims  about  for  a  time,  and  finally 
develops  another  Vaucheria  body  (Figs.  9,  B,  10). 
It  should  be  said  that  this  large  body,  called 
a  zoospore  and  acting  like  one,  is  really  a 
mass  of  small  biciliate  zoospores,  just  as  the 


«» 


Fig.  10.  A  young  Vaucheria  germinating  from  a 
spore  (sp),  and  showing  the  holdfast  {w}.— 
After  Sachs. 

apparently  one-celled  vegetative  body  is  really  composed  of 
many  cells.  In  this  large  compound  zoospore  there  are 
many  nuclei,  and  in  connection  with  each  nucleus  two  cilia 
are  developed.  Each  nucleus  with  its  cytoplasm  and  two 
cilia  represents  a  small  biciliate  zoospore,  such  as  those  of 
Cladophora,  §  24. 

Antheridia  and  oogonia  are  also  developed.  In  a  com- 
mon form  these  two  sex  organs  appear  as  short  special 
branches  developed  on  the  side  of  the  large  coenocytic  body. 


28 


PLANT   STEUCTUEES 


and  cut  off  from  the  general  cavity  by  partition  walls  (Fig. 
11).     The  oogonium  becomes  a  globular  cell,  which  usually 


Fig.  U.  Ymicheria  sessUis,  a  Siphon  form,  show- 
ing a  portion  of  the  coenocytic  body,  an  an- 
theridial  branch  (A)  with  an  empty  anthe- 
ridium  ia)  at  its  tip,  and  an  oogonium  (B) 
containing  an  oospore  (c)  and  showing  the 
opening  (/)  through  which  the  sperms  passed 
to  reach  the  egg.— Caldwell, 


develops  a  perforated  beak  for 
the  entrance  of  the  sperms,  and 
organizes  within  itself  a  single 
large  egg  (Fig.  11,  B).  The  an- 
theridium  is  a  much  smaller  cell, 
within  which  numerous  very  small 
sperms  are  formed  (Fig.  11,  A,  a). 
The  sperms  are  discharged,  swarm 
about  the  oogonium,  and  finally 
one  passes  through  the  beak  and 
fuses  with  the  egg,  the  result  be- 
ing an  oospore.  The  oospore  or- 
ganizes a  thick  wall  and  becomes 
a  resting  spore. 

It  is  evident  that  Vaucheria  is  heterogamous,  but  all  the 
other  Siphon  forms  are  isogamous,  of  which  Botrydium  may 
be  taken  as  an  illustration  (Fig.  12). 

26.  Spirogyra. — This  is  one  of  the  commonest  of  the 
"pond  scums,"  occurring  in  slippery  and  often  frothy 
masses  of  delicate  filaments  floating  in  still  water  or  about 


Fig.  12.  Botrydium,  one  of  the 
Siphon  forms  of  green  algae, 
the  whole  body  containing 
one  continuous  cavity,  with 
a  bulbous,  chlorophyll-con- 
taining portion,  and  root- 
like  branches  which  pene- 
trate the  mud  in  which 
the  plant  grows.  —  Cald- 
well. 


THE   GREAT   GRODPS   OF   ALG^ 


29 


springs.     The  filaments  are  simple,  and  are  not  anchored 
by  a  special  basal  cell,  as  in  Ulothrix  and  (Edogotiium.     The 


Fig.  13.  Spirogyra.  a  Conjugate  form,  showing  one  complete  cell  and  portions  of 
two  others.  The  band-like  chloroplasls  extend  in  a  spiral  from  one  end  of  the 
cell  to  the  other,  in  them  are  imbedded  nodule-like  bodies  (pyrenokls),  and  near 
the  center  of  the  cell  the  nucleus  is  swung  by  radiating  strands  of  cytoplasm. — 
Caldwell. 

cells  contain  remarkable  chloroplasts,  which  are  bands  pass- 
ing spirally  about  within  the  cell  wall.     These  bands  may 


Fig.  14.  Spir-ogyra,  showing  conjugation  :  A,  conjugating  tubes  approaching  each 
other;  B,  tubes  in  contact  but  end  walls  not  absorbed:  C.  tube  complete  and  con- 
tents of  one  cell  passing  through;  D,  a  completed  zygospore. — Caldwell. 


30 


PLANT   STKUCTUEES 


be  solitary  or  several  in  a  cell,  and  form  very  striking  and 
conspicuous  objects  (Figs.  13,  14), 

Spirogyra  and  its  associates  are  further  peculiar  in  pro- 
ducing no  asexual  spores,  and  also  in  the  method  of  sexual 
reproduction.  Two  adjacent  filaments  put  out  tubular 
processes  toward  one  another.  A  cell  of  one  filament  sends 
out  a  process  which  seeks  to  meet  a  corresponding  process 
from  a  cell  of  the  other  filament.  When  the  tips  of  two 
such   processes  come   together,   the   end  walls   disappear. 


Fig.  15.  Splrogyra,  showing  some  common  exceptions.  At  A  two  cells  have  been 
connected  by  a  tube,  but  without  fusion  a  zygote  has  been  organized  in  each  cell; 
also,  the  upper  cell  to  the  left  has  attempted  to  conjugate  with  the  cell  to  the 
right.  At  B  there  are  cells  from  three  filaments,  the  cells  of  the  central  one  hav- 
ing conjugated  with  both  of  the  others.— Caldwell. 


and  a  continuous  tube  extending  between  the  two  cells  is 
organized  (Figs.  14,  15).  When  many  of  the  cells  of  two 
parallel  filaments  become  thus  united,  the  appearance  is 
that  of  a  ladder,  with  the  filaments  as  the  side  pieces,  and 
the  connecting  tubes  as  the  rounds. 

While  the  connecting  tube  is  being  developed  the  con- 
tents of  the  two  cells  are  organizing,  and  after  the  comple- 
tion of  the  tube  the  contents  of  one  cell  pass  through  and 
enter  the  other  cell,  fuse  with  its  contents,  and  a  sexual 


THE   GREAT   GEOCJPS   OF  ALG^ 


31 


spore  is  organized.  As  the  gametes 
look  alike,  the  process  is  conjuga- 
tion, and  the  sex  spore  is  a  zygote, 
which,  with  its  heavy  wall,  is  rec- 
ognized to  be  a  resting  spore.  At 
the  beginning  of  each  growing 
season,  the  well-protected  zygotes 
which  have  endured  the  winter 
germinate  directly  into  new  Spi- 
rogyra  filaments. 

On  account  of  this  peculiar 
style  of  sexual  reproduction,  in 
which  gametes  are  not  discharged, 
but  reach  each  other  through  spe- 
cial tubes,  Spirogyra  and  its  allies 
are  called  Conjugate  forms — that 
is,  forms  whose  bodies  are  "  yoked 
together  "  during  the  fusion  of  the 
gametes. 

In  some  of  the  Conjugate  forms 
the  zygote  is  formed  in  the  connect- 
ing tube  (Fig.  16,  A),  and  some- 
times zygotes  are  formed  without 
conjugation  (Fig.  16,  B).  Among 
the  Conjugate  forms  the  Desmids 
are  of  great  interest  and  beauty, 
being  one-celled,  the  cells  being 
organized  into  two  distinct  halves 
(Fig.  17). 

27.  Conclusions.  —  The  Green 
Algae,  as  indicated  by  the  illustra- 
tions given  above,  include  simple 
one-celled  forms  which  reproduce 
by  fission,  but  they  are  chiefly  fila- 
mentous forms,  simple  or  branching.  These  filamentous 
bodies  either  have  the  cells  separated  from  one  another 


Fig.  16.  Two  Conjugate  forms  : 
A  (Mougeotia),  showing  for- 
mation of  zygote  in  conjuga- 
ting tube  ;  B,  C  (Gonatone- 
ma),  showing  formation  of 
zygote  without  conjugation. 
—After  WiTTROCK. 


32 


PLANT   STRUCTUEES 


by  walls,  or  they  are  coenocytic,  as  in  the  Siphon  forms. 
The  characteristic  asexual  spores  are  zoospores,  but  these 
may  be  wanting,  as  in  the  Conjugate  forms.  In  addition 
to  asexual  reproduction,  both  isogamy  and  heterogamy  are 
developed,  and  both  zygotes  and  oospores  are  resting  spores. 


Fig.  17.    A  group  of  Desmids,  one-celled  Conjugate  forms,  showing  various  pat- 
terns, and  the  cells  organized  into  distinct  halves. — After  Kerneb. 

The  Green  Algge  are  of  special  interest  in  connection 
with  the  evolution  of  higher  plants,  which  are  supposed  by 
some  to  have  been  derived  from  them. 


3.  PiT.EOPHYCE^  {Brown  Algm) 

28.  General  characters. — The  Blue-green  Algae  and  the 
Green  Algfe  are  characteristic  of  fresh  water,  but  the  Brown 
Algse,  or  "kelps,"  are  almost  all  marine,  being  very  charac- 


THE   GREAT   GROUPS   OF   ALG^ 


33 


teristic  coast  forms.  All  of  them  are  anchored  by  holdfasts, 
which  are  sometimes  highly  developed  root-like  structures ; 
and  the  yellow,  brown,  or  olive-green  floating 
bodies  are  buoyed  in  the  water  usually  by  the 
aid  of  floats  or  air-bladders,  which  are  often 
very  conspicuous.  The  kelps  are  most  highly 
developed  in  the  colder  waters,  and  form  much 
of  the  "wrack,"  "tangle,"  etc.,  of  the  coasts. 
The  group  is  well  adapted  to 
live  exposed  to  waves  and  cur- 
rents with  its  strong  holdfasts, 
air-bladders,  and  tough  leathery 
bodies.  Certain  Brown  Algae,  as 
Ectocarpus  (Fig.  18), are  of  great 
interest  on  account  of  their  pos- 
sible relation  to  the  evolution  of 
higher  plants.  It  is 
in  this  group  that  we 
have  found  our  only 
suggestions  as  to  the 
origin  of  the  complex 
sex-organs  occurring 
in  Bryophytes  and 
Pteridophytes. 

29.  The  plant 
body. — There  is  very 
great  diversity  in  the 
structure  of  the 
plant  body.  Some 
of  them,  as  Edocar- 
pus  (Fig.  18),  are  fil- 
amentous forms,  like 
the  Confervas  among 
the  Green  Alga?,  but 

others  are  very  much  more  complex.     The  thallus  of  Lam- 
inaria  is  like  a  huge  floating  leaf,  frequently  nine  to  ten 


Fig.  18.  A  browu  alga  (Ectocarini^),  showing  a 
body  consisting  of  a  simple  filament  which  puts 
out  branches  (A),  some  sporangia  iB)  contain- 
ing zoospores,  and  gametangia  {C)  containing 
gametes.— Caldwell. 


^^^ 


Flo.  18a.    A  group  of  brown  seaweeds  (Laminarias).    Note  the  various  habits  of 
the  plant  body  with  its  leaf-like  thallus  and  root-like  holdfasts.— After  Keuneb. 


THE   GREAT   GROUrS   OF   ALG^ 


35 


feet  long,  whose  stalk  develops  root-like  holdfasts  (Fig.  18a). 
The  largest  body  is  developed  by  an  Antarctic  Laminaria 
form,  which  rises  to  the  surface  from  a  sloping  bottom  with 
a  floating  thallus  six  hundred  to  nine  hundred  feet  long. 
Other  forms  rise  from  the  sea  bottom  like  trees,  with 
thick  trunks,  numerous  branches,  and  leaf-like  appendages. 

The  common  Fucus^ 
or  "  rock  weed,"  is  rib- 
bon-form and  constantly 
branches  by  forking  at 
the  tip  (Fig.  19).  This 
method  of  branching  is 
called  dichotomous,  as  dis- 
tinct from  that  in  which 
branches  are  put  out 
from  the  sides  of  the  axis 
{monojjodial).  The  swol- 
len air-bladders  distrib- 
uted throughout  the  body 
are  very  conspicuous. 

The  most  differenti- 
ated thallus  is  that  of 
Sargassum  (Fig.  20),  or 
"  gulf  weed,"  in  which 
there  are  slender  branch- 
ing stem-like  axes  bearing 
lateral  members  of  various 
kinds,  some  of"  them  like 
ordinary  foliage  leaves ; 
others  are  floats  or  air- 
bladders,  which  sometimes 

resemble  clusters  of  berries ;  and  other  branches  bear  the 
sex  organs.  All  of  these  structures  are  but  different  regions 
of  a  branching  thallus.  Sargassum  forms  are  often  torn 
from  their  anchorage  by  the  waves  and  carried  away  from 
the  coast  by  currents,  collecting  in  the  great  sea  eddies 


Fig.  19.  Fragment  of  a  common  brown 
alga  (Fucus),  showing  the  body  with 
dichotomous  branching  and  bladder-like 
air-bladders.— After  Luerssen. 


36 


PLANT   STRUCTURES 


produced  by  oceanic  currents  and  forming  the   so-called 
"  Sargasso  seas,"  as  that  of  the  North  Atlantic. 


Fig.  20.  A  portion  of  a  brown  alga  (Sargassum),  showing  the  thallus  differentiated 
into  stem-like  and  leaf-like  portions,  and  also  the  bladder-like  floats.— After  Ben- 
nett and  Murray. 


30.  Reproduction. — The  two  main  groups  of  Brown  Algae 
differ  from  each  other  in  their  reproduction.  One,  repre- 
sented by  the  Laminarias  and  a  majority  of  the  forms,  pro- 
duces zoospores  and  is  isogamous  (Fig.  18).  The  zoospores 
and  gametes  are  peculiar  in  having  the  two  cilia  attached 
at  one  side  rather  than  at  an  end ;  and  they  resemble  each 
other  very  closely,  except  that  the  gametes  fuse  in  pairs  and 
form  zygotes. 


^ 


H  > 


Fig.  21.  Sexual  reproduction  of  Fncus,  showing  the  eight  eggs  (six  in  sight)  dis- 
charged from  the  oogonium  and  surrounded  by  a  membrane  (^4),  eggs  liberated 
from  the  membrane  (E),  antheridium  containing  sperms  (C),  the  discharged  lat- 
erally biciliate  sperms  (G),  and  eggs  surrounded  by  swarming  sperms  {F,  H).— 
After  Singer. 


21 


S8 


PLANT   STRUCTURES 


The  other  group,  represented  by  Fucus  (Fig.  21),  pro- 
duces no  asexual  spores,  but  is  heterogamous.  A  single 
oogomum  usually  forms  eight  eggs  (Fig.  21,  A),  which  are 
discharged  and  float  freely  in  the  water  (Fig.  21,  E).  The 
antheridia  (Fig.  21,  C)  produce  numerous  minute  laterally 
biciliate  sperms,  which  are  discharged  (Fig.  21,  G),  swim  in 
great  numbers  about  the  large  eggs  (Fig.  21,  F^  H),  and 
finally  one  fuses  with  an  egg,  and  an  oospore  is  formed. 
As  the  sperms  swarm  very  actively  about  the  egg  and 
impinge  against  it  they  often  set  it  rotating.  Both  an- 
theridia and  oogonia  are  formed  in  cavities  of  the  thallus. 

4.  Rhodophtce^e  {Red  Algce) 
31.  General  characters. — On  account  of  their  red  colora- 
tion these  forms  are  often  called  Floridece.    They  are  mostly 

marine   forms,  and  are 

it 


anchored  by  holdfasts 
of  various  kinds.  They 
belong  to  the  deepest 
waters  in  which  Algae 
grow,  and  it  is  probable 
that  the  red  coloring 
matter  which  character- 
izes them  is  associated 
with  the  depth  at  which 
they  live.  The  Eed 
Algae  are  also  a  high- 
ly specialized  line,  and 
will  be  mentioned  very 
briefly. 

32.   The  plant  body. 
—  The    Eed    Alga3,    in 
general,  are  more  deli- 
cate   than    the    Brown 
Algfe,  or  kelps,  their  graceful  forms,  delicate  texture,  and 
brightly  tinted  bodies  (shades  of  red,  violet,  dark  purple, 


?i6.  22.  A  red  alga  {Gigai-tina),  showing 
branching  habit,  and  "fruit  bodies." — 
After  ScHENCK. 


Fig.  24.    A  red  alga  (Dasya),  showing  a  finely  divided  thallus  body. 
Caldwell. 


Fig.  25.    A  red  alga  (Rabdonia).  showiui,'  luiklfa.^t.s  and  linmrliiiig  thallus  body.- 

Caldwell. 


Fig.  26.    A  red  alga  (Ptilota),  whose  branching  body  resembles  moss. — 
Caldwell. 


THE   GREAT   GROUPS   OF   ALG^ 


43 


and  reddish-brown)  making  them  very  attractive.  They 
show  the  greatest  variety  of  forms,  branching  filaments, 
ribbons,  and  filmy  plates  prevailing,  sometimes  branching 
very  profusely  and  delicately,  and  resembling  mosses  of 
fine  texture  (Figs.  23,  23,  24,  25,  26).  The  differentiation 
of  the  thallus  into  root  and  stem  and  leaf-like  structures 
is  also  common,  as  in  the  Brown  Algae. 

33.  Reproduction. — Red  Alg^e  are  very  peculiar  in  both 
their  asexual  and  sexual  reproduction.  A  sporangium  pro- 
duces just  four  asexual  spores,  but  they  have  no  cilia  and 
no  power  of  motion.  They 
can  not  be  called  zoospores, 
therefore,  and  as    each    spo- 


FiG.  27.  A  red  alga  ( Callithamnion),  show- 
ing sporangium  (A),  and  the  tetraspores 
discharged  (iJ).— After  Thuket. 


Fig.  28.  A  red  alga  (Nemalion) ;  A, 
sexual  branches,  showing  antheri- 
dia  (a),  oogonium  (o)  with  its  trich- 
ogyne  (t),  to  which  are  attached  two 
epermatia  (s);  B,  beginning  of  a 
cystocarp  (o),  the  trichogyne  (0  still 
showing;  C,  an  almost  mature  cj's- 
tocarp  (0),  with  the  disorganizing 
trichogyne  (<). — After  Knt. 


rangium  always  produces  just 
four,  they  have  been  called 
tetraspores  (Fig.  27). 

Eed  Algaj  are  also  heterog- 
amous,  but  the  sexual  process  has  been  so  much  and  so 
variously  modified  that  it  is  very  poorly  understood.  The 
antheridia  (Fig.  28,  ^,  a)  develop  sperms  which,  like  the 
tetraspores,  have  no  cilia  and  no  power  of  motion.     To  dis- 


44 


PLANT   STRUCTURES 


tinguish  them  from  the  ciliated  sperms,  or  spermatozoids, 
which  have  the  power  of  locomotion,  these  motionless  male 
gametes  of  the  Eed  Algse  are  usually  called  sjpermatia 
(singular,  spermatiwn)  (Fig.  28,  A,  s). 

The  oogonium  is  very  pe- 
culiar, being  differentiated 
into  two  regions,  a  bulbous 
base  and  a  hair-like  process 
(trichogyne),  the  whole  struc- 
ture resembling  a  flask  with  a 
long,  narrow  neck,  excepting 
that  it  is  closed  (Fig.  28,  A, 
0,  t).  Within  the  bulbous  part 
fertilization  usually  takes 
place  ;  a  spermatium  attaches 
itself  to  the  trichogyne  (Fig. 
28,  A,  s);  at  the  point  of 
contact  the  two  walls  become 
perforated,  and  the  contents 
of  the  spermatium  thus  enter 
the  trichogyne,  and  so  reach 
the  bulbous  base  of  the  oogo- 
nium. The  above  account  rep- 
resents the  very  simplest  con- 
ditions of  the  process  of  fer- 
tilization in  this  group,  and 
gives  no  idea  of  the  great  and 
puzzling  complexity  exhibited 
by  the  majority  of  forms. 

After  fertilization  the  trich- 
ogyne wilts,  and  the  bulbous 
base  in  one  way  or  another 
develops  a  conspicuous  struc- 
ture called  the  cijstocarp  (Figs.  28,  29),  which  is  a  case  con- 
taining asexual  spores ;  in  other  words,  a  spore  case,  or  kind 
of  sporangium.     In  the  life  history  of  a  red  alga,  there- 


FiG.  29.  A  branch  of  Polyslphonia, 
one  of  the  red  algm,  showing  the 
rows  of  cells  composing  the  body 
{A),  small  branches  or  hairs  {B), 
and  a  cystocarp  (C)  with  escaping 
spores  {D)  which  have  no  cilia  (car- 
pospores). — Caldweix. 


THE  GREAT  GROUPS  OF  ALG.E 


45 


foro,  two  sorts  of  asexual  spores  are  produced :  (1)  the 
tetrasjmres,  developed  in  ordinary  sporangia ;  and  (8)  the 
carpospores,  developed  in  the  cystocarp,  which  has  been 
produced  as  the  result  of  fertilization. 

OTHER   CHLOROPHYLL-CONTAIlSriNG   THALLOPHYTES 

34.  Diatoms. — These  are  peculiar  one-celled  forms,  which 
occur  in  very  great  abundance  in  fresh  and  salt  waters. 


Fig.  30.  A  group  of  Diatoms  :  c  and  d,  top  and  side  views  of  the  same  form;  e,  colony 
of  stalked  forms  attached  to  an  alga; /and  gf,  top  and  side  views  of  the  form  shown 
at  e;  A,  a  colony;  i,  a  colony,  the  top  and  side  view  shown  at  X;.— After  Kerneu. 


They  are  either  free-swimming  or  attached  by  gelatinous 
stalks;  solitary,  or  connected  in  bands  or  chains,  or  im- 
bedded in  gelatinous  tubes  or  masses.  In  form  they  are 
rod-shaped,  boat-shaped,  elliptical,  wedge-shaped,  straight 
or  curved  (Fig.  30). 


46 


PLANT   STRUCTURES 


The  chief  peculiarity  is  that  the  wall  is  composed  of  two 
valves,  one  of  which  fits  into  the  other  like  the  two  parts  of 
a  pill  box.  This  wall  is  so  impregnated  with  silica  that  it 
is  practically  indestructible,  and  siliceous  skeletons  of  dia- 
toms are  preserved  abundantly  in  certain  rock  deposits. 
They  multiply  by  cell  division  in  a  peculiar  way,  and  some 
of  them  have  been  observed  to  con- 
jugate. 

They  occur  in  such  numbers  in  the 
ocean  that  they  form  a  large  part  of 
the  free-swimming  forms  on  the  sur- 
face of  the  sea,  and  doubtless  showers 
of  the  siliceous  skeletons  are  constant- 
ly falling  on  the  sea  bottom.  There 
are  certain  deposits  known  as  "si- 
liceous earths,"  which  are  simply 
masses  of  fossil  diatoms. 

Diatoms  have  been  variously  placed 
in  schemes  of  classification.  Some 
have  put  them  among  the  Brown 
Algae  because  they  contain  a  brown 
coloring  matter;  others  have  placed 
them  in  the  Conjugate  forms  among 
the  Green  Algae  on  account  of  the 
occasional  conjugation  that  has  been 
observed.  They  are  so  different  from 
other  forms,  however,  that  it  seems 
best  to  keep  them  separate  from  all 
other  Algae. 

35.  Characese. — These  are  common- 
ly called  "  stoneworts,"  and  are  often 
included  as  a  group  of  Green  Algae, 
as  they  seem  to  be  Thallophytes,  and 
have  no  other  coloring  matter  than 
chlorophyll.  However,  they  are  so  peculiar  that  they  are 
better  kept  by  themselves  among  the  Algse.    They  are  such 


Fig.  31.  A  common  Chara, 
showing  tip  of  main  axis. 
— After  Strasburger. 


THE   GKEAT   GROUPS   OF   ALG^  47 

specialized  forms,  and  are  so  much  more  highly  organized 
than  all  other  Algae,  that  they  will  be  passed  over  here  with 
a  bare  mention.  They  grow  in  fresh  or  brackish  waters, 
fixed  to  the  bottom,  and  forming  great  masses.  The  cylin- 
drical stems  are  Jointed,  the  joints  sending  out  circles  of 
branches,  which  repeat  the  jointed  and  branching  habit 
(Fig.  31). 

The  walls  become  incrusted  with  a  deposit  of  lime, 
which  makes  the  plants  harsh  and  brittle,  and  has  sug- 
gested the  name  "  stoneworts."  In  addition  to  the  highly 
organized  nutritive  body,  the  antheridia  and  oogonia  are 
peculiarly  complex,  being  entirely  unlike  the  simple  sex 
organs  of  the  other  Algge. 


CHAPTEE  V 

THALLOPHYTES :  FUNGI 

36.  General  characters. — In  general,  Fungi  include-  Thal- 
lophytes  whicli  do  not  contain  chlorophyll.  From  this  fact 
it  follows  that  they  can  not  manufacture  food  entirely  out 
of  inorganic  material,  but  are  dependent  for  it  upon  other 
plants  or  animals.  This  food  is  obtained  in  two  general 
ways,  either  (1)  directly  from  the  living  bodies  of  plants  or 
animals,  or  (2)  from  dead  bodies  or  the  products  of  living 
bodies.  In  the  first  case,  in  which  living  bodies  are  at- 
tacked, the  attacking  fungus  is  called  a  imrasite^  and  the 
plant  or  animal  attacked  is  called  the  liod.  In  the  second 
case,  in  which  living  bodies  are  not  attacked,  the  fungus  is 
called  a  saprophyte.  Some  Fungi  can  live  only  as  parasites, 
or  as  saprophytes,  but  some  can  live  in  either  way. 

Fungi  form  a  very  large  assemblage  of  plants,  much 
more  numerous  than  the  Alg^.  As  many  of  the  parasites 
attack  and  injure  useful  plants  and  animals,  producing 
many  of  the  so-called  "  diseases,"  they  are  forms  of  great 
interest.  Governments  and  Experiment  Stations  have  ex- 
pended a  great  deal  of  money  in  studying  the  injurious 
parasitic  Fungi,  and  in  trying  to  discover  some  method  of 
destroying  them  or  of  preventing  their  attacks.  Many  of 
the  parasitic  forms,  however,  are  harmless ;  while  many  of 
the  saprophytic  forms  are  decidedly  beneficial. 

It  is  generally  supposed  that  the  Fungi  are  derived  from 
the  Algffi,  having  lost  their  chlorophyll  and  power  of  inde- 
pendent living.  Some  of  them  resemble  certain  Alga?  so 
closely  that  the  connection  seems  very  plain;  but  others 


THALLOrilYTES:  FUNGI 


49 


have  been  so  modified  by  their  parasitic  and  saprophytic 
habits  that  they  have  lost  all  likeness  to  the  Algs,  and 
their  connection  with  them  is  very  obscure. 

37.  The  plant  body. — Discarding  certain  problematical 
forms,  to  be  mentioned  later,  the  bodies  of  all  true  Fungi 
are  organized  upon  a  uniform  general  plan,  to  which  they 
can  all  be  referred  (Fig.  32).     A  set  of  colorless  branching 


Pig.  33.  A  diagrammatic  representation  of  Mvcm\  showing  the  profusely  branching 
mycelium,  and  three  vertical  hyphse  (sporophores),  sporangia  forming  on  b  and  c. 
— After  Zopp. 


filaments,  either  isolated  or  interwoven,  forms  the  main 
working  body,  and  is  called  the  mycelium.  The  interweav- 
ing may  be  very  loose,  the  mycelium  looking  like  a  delicate 
cobweb ;  or  it  may  be  close  and  compact,  forming  a  felt-like 
mass,  as  may  often  be  seen  in  connection  with  preserved 
fruits.  The  individual  threads  are  called  liy])h(B  (singular, 
liyplia)  or  liyplial  threads.  The  mycelium  is  in  contact  with 
its  source  of  food  supply,  which  is  called  the  substratum. 


50  PLANT  STRUCTDEES 

From  the  hyphal  threads  composing  the  mycelium  verti- 
cal ascending  branches  arise,  which  are  set  apart  to  produce 
the  asexual  spores,  which  are  scattered  and  produce  new 
mycelia.  These  branches  are  called  ascending  liyplicR  or 
sporoplwres,  meaning  "  spore  bearers." 

Sometimes,  especially  in  the  case  of  parasites,  special 
descending  branches  are  formed,  which  penetrate  the  sub- 
stratum or  host  and  absorb  the  food  material.  These  spe- 
cial absorbing  branches  are  called  liaustoria,  meaning  "  ab- 
sorbers." 

Such  a  mycelial  body,  with  its  sporophores,  and  perhaps 
haustoria,  lies  either  upon  or  within  a  dead  substratum  in 
the  case  of  saprophytes,  or  vipon  or  within  a  living  plant  or 
animal  in  the  case  of  parasites. 

38.  The  subdivisions. — The  classification  of  Fungi  is  in 
confusion  on  account  of  lack  of  knowledge.  They  are  so 
much  modified  by  their  peculiar  life  habits  that  they  have 
lost  or  disguised  the  structures  which  prove  most  helpful  in 
classification  among  the  Algae.  Four  groups  will  be  pre- 
sented, often  made  to  include  all  the  Fungi,  but  doubtless 
they  are  insuflHcient  and  more  or  less  unnatural. 

The  constant  termination  of  the  group  names  is  mycetes, 
a  Greek  word  meaning  "  fungi."  The  prefix  in  each  case  is 
intended  to  indicate  some  important  character  of  the  group. 
The  names  of  the  four  groups  to  be  presented  are  as  follows : 
(1)  Pliymmycetes  ("  Alga-Fungi "),  referring  to  the  fact 
that  the  forms  plainly  resemble  the  Algse  ;  (2)  Ascomycetes 
("  Ascus-Fungi  ") ;  (3)  ^Ecidiomycetes  ("^cidium-Fungi  ") ; 
(4)  Basidiomycetes  ("  Basidium-Fungi ").  Just  what  the 
prefixes  ascus,  cecidium,  and  lasidium  mean  will  be  ex- 
plained in  connection  with  the  groups.  The  last  three 
groups  are  often  associated  together  under  the  name  My- 
comycetes,  meaning  "  Fungus-Fungi,"  to  distinguish  them 
from  the  Phycomycetes,  or  "  Alga-Fungi,"  referring  to  the 
fact  that  they  do  not  resemble  the  Algae,  and  are  only  like 
themselves. 


THALLOPHYTES:  FUNGI  5]^ 

One  of  the  ordinary  life  processes  which  seems  to  be 
seriously  interfered  with  by  the  saprophytic  and  parasitic 
habit  is  the  sexual  process.  At  least,  while  sex  organs 
and  sexual  spores  are  about  as  evident  in  Phycomycetes 
as  in  Alga3,  they  are  either  obscure  or  wanting  in  the 
Mycomycete  groups. 

1.  Phycomycetes  {Alga-Fungi) 

39.  Saprolegnia. — This  is  a  group  of  "  water-moulds," 
with  aquatic  liabit  like  the  Alg«.  They  live  upon  the  dead 
bodies  of  water  plants  and  animals  (Fig.  33),  and  some- 
times attack  living  fish,  one  kind  being  very  destructive 
to  young  fish  in  hatcheries.  The  hyphaj  composing  the 
mycelium  are  coenocytes,  as  in  the  Siphon  forms. 

Sporangia  are  organized  at  the  ends  of  branches  by 
forming  a  partition  wall  separating  the  cavity  of  the  tip 
from  the  general  cavity  (Pig-  33,  B).  The  tip  becomes 
more  or  less  swollen,  and  within  it  are  formed  numerous 
biciliate  zoospores,  which  are  discharged  into  the  water 
(Fig.  33,  C),  swim  about  for  a  short  time,  and  rapidly  form 
new  mycelia.  The  process  is  very  suggestive  of  Cladopliora 
and  Vaucheria.  Oogonia  and  antheridia  are  also  formed 
at  the  ends  of  the  branches  (Fig.  33,  F),  much  as  in  Vau- 
cheria. The  oogonia  are  spherical,  and  form  one  and  some- 
times many  eggs  (Fig.  33,  i),  E).  The  antheridia  are 
formed  on  branches  near  the  oogonia.  An  antheridium 
comes  in  contact  with  an  oogonium,  and  sends  out  a  deli- 
cate tube  which  pierces  the  oogonium  wall  (Fig.  33,  F). 
Through  this  tube  the  contents  of  the  antheridium  pass, 
fuse  with  the  egg.,  and  a  heavy-walled  oospore  or  resting 
spore  is  the  result. 

It  is  an  interesting  fact  that  sometimes  the  contents  of 
an  antheridium  do  not  enter  an  oogonium,  or  antheridia 
may  not  even  be  formed,  and  still  the  egg.,  without  fertiliza- 
tion, forms  an  oospore  which  can  germinate.     This  peculiar 


52 


PLANT  STRUCTURES 


habit  is  called  imrthenogenesis^  which  means  reproduction 
by  an  Qgg  without  fertilization. 


Fig.  33.  A  common  water  mould  (Saprolegina):  A,  a  fly  from  which  mycelial  fila- 
ments of  the  parasite  aregrowing;  B,  tip  of  a  branch  organized  as  a  sporangium; 
C  sporangium  discharging  biciliate  zoospores;  F.  oogonium  with  antheridium  in 
contact,  the  tube  having  penetrated  to  the  egg;  D  and  E,  oogonia  with  several 
eggs.— ^-C  after  Thuret.  D-F  nUer  DeBary. 


40.  Mucor. — One  of  the  most  common  of  the  Mucors,  or 
"  black  moulds,"  forms  white  furry  growths  on  damp  bread, 
preserved  fruits,  manure  heaps,  etc.  It  is  therefore  a 
saprophyte,  the  coenocytic  mycelium  branching  extensively 
through  the  substratum  (Fig.  34). 


THALLOPHYTES:  FUNGI 


53 


Erect  sporophores  arise  from  it  in  abundance,  and  at 
the  top  of  each  sporophore  a  globular  sporangium  is  formed, 
within  which  are  numerous  small  asexual  spores  (Figs.  35, 


Fig.  34.    Diagram  showing  mycelium  and  sporophores  of  a  common  Mucor. — 
Cald'well. 


36).  The  sporangium  wall  bursts  (Fig.  37),  the  light  spores 
are  scattered  by  the  wind,  and,  falling  upon  a  suitable  sub- 
stratum,   germinate    and 


form  new  mycelia.  It  is 
evident  that  these  asex- 
ual spores  are  not  zoo- 
spores, for  there  is  no 
water  medium  and  swim- 
ming is  impossible.  This 
method  of  transfer  being 
impossible,  the  spores  are 
scattered  by  currents  of 
air,  and  must  be  corre- 
spondingly light  and  pow- 
dery. They  are  usually 
spoken  of  simply  as 
"  spores,"  without  any 
prefix. 

22 


Fig.  35.  Forming  sporangia  of  Mucor,  show- 
ing the  swollen  tip  of  the  sporophore  (^4), 
and  a  later  stage  (B),  in  which  a  wall  is 
formed  separating  the  sporangium  from 
the  rest  of  the  body.— Caldwell. 


54 


PLANT   STRDCTUEES 


While  the  ordinary  method  of  reproduction  through  the 
growing  season  is  by  means  of  these  rapidly  germinating 
spores,  in  certain  conditions  a  sexual  process  is  observed, 
by  which  a  heavy-walled  sexual  spore  is  formed  as  a  resting 
spore,  able  to  outlive  unfavorable  conditions.  Branches 
arise  from  the  hyphge  of  the  mycelium  just  as  in  the  forma- 


FiQ.  36.  Mature  sporangium  of  Mucor,  showing 
the  wall  {A),  the  numerous  spores  (C),  and 
the  columella  {B) — that  is,  the  partition  wall 
pushed  up  into  the  cavity  of  the  sporangium. 
—Caldwell. 


Fig.  37.  Bursted  sporangium  of 
Mucor,  the  ruptured  wall  not 
being  shown,  and  the  loose 
spores  adhering  to  the  colu- 
mella.—Caldwell. 


tion  of  sporophores  (Fig.  38).  Two  contiguous  branches 
come  in  contact  by  their  tips  (Fig.  38,  A),  the  tips  are  cut 
oS  from  the  main  coenocytic  body  by  partition  walls  (Fig. 
38,  i?),  the  walls  in  contact  disorganize,  the  contents  of 
the  two  tip  cells  fuse,  and  a  heavy-walled  sexual  spore  is 
the  result  (Fig.  38,  C).  It  is  evident  that  the  process  is 
conjugation,  suggesting  the  Conjugate  forms  among  the 


THALLOPHYTES:  FUNGI 


55 


Algse  ;  that  the  sexual  spore  is  a  zygote  ;  and  that  the  two 
pairing  tip  cells  cut  ofE  from  the  main  body  by  partition 
walls  are  gametangia.     uMucor,  therefore,  is  isogamous. 


Fig.  38.  Sexual  reproduction  of  Mucor,  showing  tips  of  sex  branches  meeting  (A), 
the  two  gametangia  cut  off  by  partition  walls  (J5),  and  the  heavy-walled  zygote 
(C)-— Caldwell. 


41.  Peronospora, — These  are  the  "  downy  mildews,"  very 
common  parasites  on  seed  plants  as  hosts,  one  of  the  most 
common  kind  attacking  grape  leaves.  The  mycelium  is  coeno- 
cytic  and  entirely  internal,  ramifying  among  the  tissues 
within  the  leaf,  and  piercing  the  living  cells  with  haustoria 
which  rapidly  absorb  their  contents  (Fig.  39).  The  pres- 
ence of  the  parasite   is   made   known  by  discolored  and 


56 


PLANT   STRUCTDRES 


finally  deadened  spots  on  the  leaves,  where  the  tissues  have 
been  killed. 

From  this  internal  mycelium  numerous  sporophores 
arise,  coming  to  the  surface  of  the  host  and  securing  the 
scattering  of  their 
spores,  which  fall 
upon  other  leaves 
and  germinate,  the 
new  mycelia  pene- 
trating among  the 
tissues  and  begin- 
ning their  ravages. 
The  sporophores,  af- 
ter rising  above  the 
surface  of  the  leaf, 

branch  freely ;  and  many  of  them  rising  near  together, 
they  form  little  velvety  patches  on  the  surface,  suggesting 
the  name  "  downy  mildew." 

b  ^ 


Fig.  39.  A  branch  of  Peronoitpora  in  contact  with 
two  cells  of  a  host  plant,  and  sending  into  them 
its  large  haustoria.— After  DeBart. 


Fig.  40.  Pei'onospora,  one  of  the  Phycomycetes,  showing  at  a  an  oogonium  (o)  con- 
taining an  egg,  and  an  antheridinm  in)  in  contact;  at  b  the  antheridial  tube  pene- 
trating the  oogonium  and  discharging  the  contents  of  the  antheridium  into  the 
egg;  at  c  the  oogonium  containing  the  oospore  or  resting  spore.— After  DeBart. 


In  certain  conditions  special  branches  arise  from  the 
mycelium,  which  organize  antheridia  and  oogonia,  and 
remain  within  the  host  (Fig.  40).  The  oogonium  is  of  the 
usual  spherical  form,  organizing  a  single  egg.      The  an- 


THALLOPHYTES:  FUNGI  5Y 

theridium  comes  in  contact  with  the  oogonium,  puts  out  a 
tube  which  pierces  the  oogonium  wall  and  enters  the  egg, 
into  which  the  contents  of  the  antheridium  are  discharged, 
and  fertilization  is  effected.  The  result  is  a  heavy-walled 
oospore.  As  the  oospores  are  not  for  immediate  germina- 
tion, they  are  not  brought  to  the  surface  of  the  host  and 
scattered,  as  are  the  asexual  spores.  When  they  are  ready 
to  germinate,  the  leaves  bearing  them  have  perished  and 
the  oospores  are  liberated. 

42.  Conclusions. — The  coenocytic  bodies  of  the  whole  group 
are  very  suggestive  of  the  Siphon  forms  among  Green  Algae, 
as  is  also  the  method  of  forming  oogonia  and  antheridia. 

The  water-moulds,  Saprolegjiia  and  its  allies,  have  re- 
tained the  aquatic  habit  of  the  Alga?,  and  their  asexual 
spores  are  zoospores.  Such  forms  as  Mucor  and  Perono- 
spora,  however,  have  adapted  themselves  to  terrestrial  con- 
ditions, zoospores  are  abandoned,  and  light  spores  are  de- 
veloped which  can  be  carried  about  by  currents  of  air. 

In  most  of  them  motile  gametes  are  abandoned.  Even 
in  the  heterogamous  forms  sperms  are  not  organized  within 
the  antheridium,  but  the  contents  of  the  antheridium  are 
discharged  through  a  tube  developed  by  the  wall  and  pene- 
trating the  oogonium.  It  should  be  said,  however,  that  a 
few  forms  in  this  group  develop  sperms,  which  make  them 
all  the  more  alga-like. 

They  are  both  isogamous  and  heterogamous,  both  zygotes 
and  oospores  being  resting  spores.  Taking  the  characters 
all  together,  it  seems  reasonably  clear  that  the  Phycomycetes 
are  an  assemblage  of  forms  derived  from  Green  Algae  (Chlo- 
rophyceae)  of  various  kinds. 

2.  AscoMYCETES  {Asci(s-  ov  Sac-Fungi) 

43.  Mildews.— These  are  very  common  parasites,  growing 
especially  upon  leaves  of  seed  plants,  the  mycelium  spread- 
ing over  the  surface  like  a  cobweb.     A  very  common  mil- 


58 


PLANT   STKUCTURES 


dew,  Microsphmra,  grows  on  lilac  leaves,  which  nearly 
always  show  the  whitish  covering  after  maturity  (Fig.  41). 
The  branching  hyphae  show  numerous  partition  walls,  and 
are  not  ccenocytic  as  in  the  Phycomycetes.  Small  disk-like 
haustoria  penetrate  into  the  superficial  cells  of  the  host, 
anchoring  the  mycelium  and  absorbing  the  cell  contents. 

Sporophores  arise,  which  form  asexual  spores  in  a  pe- 
culiar way.  The  end  of  the  sporophore  rounds  off,  almost 
separating  itself  from  the  part  below,  and  becomes  a  spore 
or  spore-like  body.      Below  this  another  organizes  in  the 

same  way,  then  another,  until 
a  chain  of  spores  is  developed, 
easily  broken  apart  and  scat- 
tered by  the  wind.  Falling 
upon  other  suitable  leaves, 
they  germinate  and  form  new 
mycelia,  enabling  the  fungus 
to  spread  rapidly.  This  meth- 
od of  cutting  a  branch  into 
sections  to  form  spores  is 
called  abstriction,  and  the 
spores  formed  in  this  way 
are  called  conidia^  or  conidi- 
ospores  (Fig.  43,  B). 

At  certain  times  the  myce- 
lium develops  special  branches 
which  develop  sex  organs,  but 
they  are  seldom  seen  and  may 
not  always  occur.     An  oogo- 
nium and  an  antheridium,  of 
the  usual  forms,  but  probably 
without   organizing   gametes, 
come  into  contact,  and  as  a 
result  an  elaborate  structure  is  developed — the  ascocarp^ 
sometimes  called  the  "  spore  fruit."     These  ascocarps  ap- 
pear on  the  lilac  leaves  as  minute  dark  dots,  each  one  being 


Fig.  41.  Lilac  leaf  covered  with  mil- 
dew {Mic)-ospha:ra),  the  shaded  re- 
gions representing  the  mycelium, 
and  the  black  dots  the  ascocarps. — 
S.  M.  Coulter. 


TIIALLOrilYTES:  FUNGI 


59 


a  little  sphere,  wliicli  suggested  the  name  Microsphmra 
(Fig.  41).  The  heavy  wall  of  the  ascocarp  bears  beauti- 
ful branching  hair-like  appendages  (Fig.  42). 

Bursting  the  wall  of  this  spore  fruit  several  very  delicate, 
bladder-like  sacs  are  extruded,  and  through  the  transparent 
wall  of  each  sac  there  may  be 
seen  several  spores  (Fig.  42). 
The  ascocarp,  therefore,  is 
a  spore  case.  Just  as  is  the 
cystocarp  of  the  Eed  Algae 
(§  33).  The  delicate  sacs 
within  are  the  asci,  a  word 
meaning  "sacs,"  and  each 
ascus  is  evidently  a  mother 
cell  within  which  asexual 
spores  are  formed.  These 
spores  are  distinguished 
from  other  asexual  spores 
by  the  name  ascospore. 

It  is  these  peculiar  moth- 
er cells,  or  asci,  which  give 
name  to  the  group,  and  an 

Ascomycete,  Ascus-fungus,  or  Sac-fungus,  is  one  which  pro- 
duces spores  in  asci ;  and  an  ascocarp  is  a  spore  case  which 
contains  asci. 

In  the  mildews,  therefore,  there  are  two  kinds  of  asexual 
spores  :  (1)  conidia,  formed  from  a  hyphal  branch  by  abstric- 
tion,  by  which  the  mycelium  may  spread  rapidly;  and  (2) 
ascospores,  formed  in  a  mother  cell  and  protected  by  a  heavy 
case,  so  that  they  may  bridge  over  unfavorable  conditions, 
and  may  germinate  when  liberated  and  form  new  mycelia. 
The  resting  stage  is  not  a  zygote  or  an  oospore,  as  in  the 
Algge  and  Phycomycetes,  no  sexual  spore  probably  being 
formed,  but  a  heavy-walled  ascocarp. 

44.  Other  forms. — The  mildews  have  been  selected  as  a 
simple  illustration  of  Ascomycetes,  but  the  group  is  a  very 


Fig.  42.  Ascocarp  of  the  lilac  mUdew, 
showing  branching  appendages  and 
two  asci  protruding  from  the  rup- 
tured wall  and  containing  ascospores. 
— S.  M.  Coulter. 


60 


PLANT   STKCCTUEES 


large  one,  and  contains  a  great  variety  of  forms.  All  of 
them,  however,  produce  spores  in  asci,  but  the  asci  are  not 
always  inclosed  by  an  ascocarp.  Here  belong  the  common 
blue  mould  {Petiicillimn),  found  on  bread,  fruit,  etc.,  in 
which  stage  the  branching  chains  of  conidia  are  very  con- 
spicuous (Fig.  43) ;  the  truffle-fungi,  upon  whose  subter- 


Fie.  43.  PenicilUum,  a  common  mould:  A,  mycelium  with  numerous  branching 
sporophores  bearing  conidia;  B,  apex  of  a  sporophore  enlarged,  showing  branch- 
ing and  chains  of  conidia. — After  Brbfeld. 


ranean  mycelia  ascocarps  develop  which  are  known  as 
"  truffles  " ;  the  black  fungi,  which  form  the  diseases  known 
as  "  black  knot  "  of  the  plum  and  cherry,  the  "  ergot  "  of 
rye  (Fig.  44),  and  many  black  wart-like  growths  upon  the 
bark  of  trees ;  other  forms  causing  "  witches'-brooms  "  (ab- 
normal growths  on  various  trees),  "  peach  curl,"  etc.,  the 
cup-fungi  (Figs.  45,  46),  and  the  edible  morels  (Fig.  47). 


THALLOPIIYTES:  FUNGI 


61 


Fis.  44.  Head  of  rye  attacked  by  "er- 
got" (a),  peculiar  grain-like  masses 
replacing  the  grains  of  rye  ;  also  a 
mass  of  "ergot"  germinating  to 
form  spores  (4).— After  Tclasne. 


Fig.  46.  A  cup-fungus  (Pitya)  grow- 
ing on  a  spruce  {Picea).  —  After 
Rehm. 


In  some  of  these  forms  the  ascocarp  is  completely  closed, 
as  in  the  lilac  mildew ;  in  others  it  is  flask-shaped  ;  in 
others,  as  in  the  cup-fungi,  it  is  like  a  cup  or  disk  ;  hut  in 
all  the  spores  are  inclosed  by  a  delicate  sac,  the  ascus. 


62 


PLANT   STRUCTURES 


Here  must  probably  be  included  the  yeast-fungi  (Fig. 
48),  so  commonly  used    to  excite  alcoholic  fermentation. 


Fig.  47.  The  common  edible  morel  (Morchella 
esctilenta).  The  structure  shown  and  used 
represents  the  ascocarp,  the  depressions  of 
whose  surface  are  lined  with  asci  contain- 
ing ascospores. — After  Gibson. 


Fig.  48.  Yeast  cells,  reprodu- 
cing by  budding,  and  form- 
ing chains.— Caldwell. 


The  "  yeast  cells  "  seem  to  be  conidia  having  a  peculiar  bud- 
ding method  of  multiplication,  and  the  remarkable  power 
of  exciting  alcoholic  fermentation  in  sugary  solutions. 

3.  ^ciDiOMYCETES  {^cidium-Fungi) 

45.  General  characters. — This  is  a  large  group  of  very 
destructive  parasites  known  as  "  rusts  "  and  "  smuts."  The 
rusts  attack  particularly  the  leaves  of  higher  plants,  pro- 
ducing rusty  spots,  the  wheat  rust  probably  being  the  best 
known.  The  smuts  especially  attack  the  grasses,  and  are 
very  injurious  to  cereals,  producing  in  the  heads  of  oats, 
barley,  wheat,  corn,  etc.,  the  disease  called  smut. 


TIIALLOPIIYTES:  FUNGI  g3 

In  some  forms  an  obscure  sexual  process  has  been  de- 
scribed, but  it  is  beyond  the  reach  of  ordinary  observation. 
The  iEcidiomycetes  do  not  form  an  independent  and  nat- 
ural group,  but  are  now  generally  placed  under  the  Basi- 
diomycetes,  but  they  are  so  unlike  the  ordinary  forms  of 
that  group  that  they  are  here  kept  distinct. 

Most  of  the  forms  are  Yerj  poly7)iorpInc — that  is,  a  plant 
assumes  several  dissimilar  appearances  in  the  course  of  its 
life  history.  These  phases  are  often  so  dissimilar  that  they 
have  been  described  as  different  plants.  This  polymorphism 
is  often  further  complicated  by  the  appearance  of  different 
phases  upon  entirely  different  hosts.  For  example,  the 
wheat-rust  fungus  in'  one  stage  lives  on  wheat,  and  in  an- 
other on  barberry. 

46.  Wheat  rust. — This  is  one  of  the  few  rusts  whose  life 
histories  have  been  traced,  and  it  may  be  taken  as  an  illus- 
tration of  the  group. 

The  mycelium  of  the  fungus  is  found  ramifying  among 
the  leaf  and  stem  tissues  of  the  wheat.  While  the  wheat  is 
growing  this  mycelium  sends  to  the  surface  numerous  spo- 


c^^^fkrm^'^(?Sfi  iliiL" 


Fig.  49.    Wheat  rust,  showing  sporophores  breaking  through  the  tissues  of  the  host 
and  bearing  summer  spores  (uredospores). — After  H.  Marshall  Ward. 

rophores,  each  bearing  at  its  apex  a  reddish  spore  (Fig.  49). 
As  the  spores  occur  in  great  numbers  they  form  the  rusty- 
looking  lines  and  spots  which  give  name  to  the  disease. 
The  spores  are  scattered  by  currents  of  air,  and  falling  upon 
other  plants,  germinate  very  promptly,  thus  spreading  the 


64 


PLANT   STRUCTUEES 


disease  with  great  rapidity  (Fig.  50).  Once  it  was  thought 
that  this  completed  the  life  cycle,  and  the  fungus  received 
the  name  Uredo.     When  it  was  known  that  this  is  but  one 


Fig.  50. — Wheat  rust,  showing  a  young  hypha  forcing  its  way  from  the  surface  of 
leaf  down  among  the  nutritive  cells. — After  H.  Marshall  Wabd. 


stage  in  a  polymorphic  life  history  it  was  called  the  Uredo- 
stage,  and  the  spores  iiredospores,  sometimes  "  summer 
spores.^' 


Fig.  51.    Wheat  rust,  showing  the  winter  spores  (teleutospores).— After 
H.  Marshall  Ward. 

Toward  the  end  of  the  summer  the  same  mycelium 
develops  sporophores  which  bear  an  entirely  different  kind 
of  spore  (Fig.  51).     It  is  two-celled,  with  a  very  heavy  black 


THALLOPIIYTES:   FUNGI 


65 


wall,  and  forms  what  is  called  the  "  black  rust,"  which  ap- 
pears late  in  the  summer  on  wheat  stubble.  Tliese  spores 
are  the  resting  spores,  which  last  through  the  winter  and 
germinate  in  the  following  spring.  They  are  called  teUuto- 
spores,  meaning  the  "  last  spores  "  of  the  growing  season. 
They  are  also  called  "  winter  spores,"  to  distinguish  them 
from  the  uredospores  or  "  summer  spores."  At  first  this 
teleutospore-bearing  mycelium  was  not  recognized  to  be 
identical  with  the  uredospore-bearing  mycelium,  and  it  was 
called  Puccinia.  This  name  is  now 
retained  for  the  whole  polymorphous 
plant,  and  wheat  rust  is  Puccinia 
granmiis.  This  mycelium  on  the 
wheat,  with  its  summer  spores  and 
winter  spores,  is  but  one  stage  in 
the  life  history  of  wheat  rust. 

In  the  spring  the  teleutospore 
germinates,  each  cell  developing  a 
small  few-celled  filament  (Fig.  53). 
From  each  cell  of  the  filament  a 
little  branch  arises  which  develops 
at  its  tip  a  small  spore,  called  a  sjjo- 
ridium,  which  means  "  spore-like." 
This  little  filament,  which  is  not  a 
parasite,  and  which  bears  sporidia, 
is  a  second  phase  of  the  wheat  rust, 
really  the  first  phase  of  the  growing 
season. 

The  sporidia  are  scattered,  fall 
upon  barberry  leaves,  germinate,  and 
develop  a  mycelium  which  spreads 

through  the  leaf.  This  mycelium  produces  sporophores 
which  emerge  on  the  under  surface  of  the  leaf  in  the 
form  of  chains  of  reddish-yellow  conidia  (Fig.  53).  These 
chains  of  conidia  are  closely  packed  in  cup-like  receptacles, 
and  these  reddish-yellow  cup-like  masses  are  often  called 


Fig.  52.  Wheat  rtist,  show- 
ing a  teleutospore  germina- 
ting and  forming  a  short  fil- 
ament, from  four  of  whose 
cells  a  spore  branch  arises, 
the  lowest  one  bearing  at 
its  tip  a  sporidinm. — After 
H.  Marshall  Ward. 


QQ 


PLANT   STRUCTURES 


"  cluster-cups."     This  mycelium  on  the  barberry,  bearing 
cluster-cups,  was  thought  to  be  a  distinct  plant,  and  was 

called  jl^Jcidium.  The 
name  now  is  applied  to 
the  cluster-cups,  which 
are  called  cecidia,  and 
the  conidia-like  spores 
which  they  produce  are 
known  as  (ecidiospores. 

It  is  the  gecidia  which 
give  name  to  the  group, 
and  ^cidiomycetes  are 
those  Fungi  in  whose 
life  history  gecidia  or 
cluster-cups  appear. 

The  ajcidiospores  are 
scattered  by  the  wind, 
fall  upon  the  spring 
wheat,  germinate,  and 
develop  again  the  myce- 
lium which  produces  the 
rust  on  the  wheat,  and 
so  the  life  cycle  is  com- 
pleted. There  are  thus 
at  least  three  distinct 
stages  in  the  life  history 
of  wheat  rust.  Begin- 
ning with  the  growing 
season  they  are  as  fol- 
lows :  (1)  The  phase  bear- 
ing the  sporidia,  which 
is  not  parasitic ;  (2)  the 
eecidium  phase,  parasitic 
on  the  barberry;  (3)  the  uredo-teleutospore  phase,  para- 
sitic on  the  wheat. 

In  this  life  cycle  at  least  four  kinds  of  asexual  spores 


TIIALLOPIIYTES:  FUNGI 


67 


appear :  (1)  sporidia,  which  develop  the  stage  on  the  barber- 
ry ;  (3)  (ecidiospores,  which  develop  the  stage  on  the  wheat ; 
(3)  uredos2iores^yfhich.  repeat  the  mycelium  on  the  wheat ;  (4) 
teleutos2)ores,yf\\\ch  last  through  the  winter,  and  in  the  spring 
produce  the  stage  bearing  sporidia.  It  should  be  said  that 
there  are  other  structures  of  this  plant  produced  on  the  bar- 
berry (Fig.  53),  but  they  are  too  uncertain  to  be  included  here. 
The  barberry  is  not  absolutely  necessary  to  this  life  cycle. 
In  many  cases  there  is  no  available  barberry  to  act  as  host, 
and  the  sporidia  germinate'directly  upon  the  young  wheat, 
forming  the  rust-producing  mycelium,  and  the  cluster-cup 
stage  is  omitted. 


Fig.  54.    Two  species  of  "cedar  apple"  {Gymnosporanglum).  both  on  the  common 
juniper  (Juniperns  Virginiana).—A  after  Farlow,  B  after  Engler  and  Prantl. 


47.  Other  rusts. — Many  rusts  have  life  histories  similar 
to  that  of  the  wheat  rust,  in  others  one  or  more  of  the 
stages  are  omitted.     In  very  few  have  the  stages  been  con- 


68 


PLANT   STRUCTDKES 


nected  together,  so  that  a  mycelium  bearing  uredospores  is 
called  a  Uredo,  one  bearing  teleutospores  a  Puceinia,  and 
one  bearing  aecidia  an  ^cidiuin  ;  but  what  forms  of  Uredo, 
Puccinia^  and  JEcidium  belong  together  in  the  same  life 
cycle  is  very  difficult  to  discover. 

Another  life  cycle  which  has  been  discovered  is  in  con- 
nection with  the  "  cedar  apples "  which  appear  on  red 
cedar  (Fig.  54).  In  the  spring  these  diseased  growths  be- 
come conspicuous,  especially  after  a  rain,  when  the  jelly- 
like masses  containing  the  orange-colored  spores  swell. 
This  corresponds  to  the  phase  which  produces  rust  in 
wheat.  On  the  leaves  of  apple  trees,  wild  crab,  hawthorn, 
etc.,  the  aecidium  stage  of  the  same  parasite  develops. 

4.  Basidiomycetes  {Basidium-Fungi). 

48.  General  characters. — This  group  includes  the  mush- 
rooms, toadstools,  and  puffballs.     They  are  not  destructive 

parasites,  as  are  many 
forms  in  the  preceding 
groups,  but  mostly  harm- 
less and  often  useful  sap- 
rophytes. They  must 
also  be  regarded  as  the 
most  highly  organized  of 
the  Fungi.  The  popular 
distinction  between  toad- 
stools and  mushrooms  is 
not  borne  out  by  botan- 
ical characters,  toadstool 
and  mushroom  being  the 
same  thing  botanically, 
and  forming  one  group, 
puffballs  forming  an- 
other. 

As  in  ^cidiomycetes, 

Fig.  55.    The  common  edible  mushroom, 
Agaricus  campestris.—Afier  Gibson.  an  obsCUre  Sexual  prOCeSS 


TIIALLOPIIYTES:  FUNGI 


69 


is  reported.  The  life  history  seems  simple,  but  this  appar- 
ent simplicity  may  represent  a  very  complicated  history. 
The  structure  of  the  common  mushroom  {Agaricus)  will 
serve  as  an  illustration  of  the  group  (Fig.  55). 

49.  A  common 
mushroom.  —  The 
mycelium,  of  white 
branching  threads, 
spreads  extensively 
through  the  decay- 
ing substratum, 
and  in  cultivated 
forms  is  spoken  of 
as  the  "  spawn." 
Upon  this  myce- 
lium little  knob- 
like protuberances 
begin  to  arise,  grow- 
ing  larger  and 
larger,  until  they 
are  organized  into 
the  so-called 
"  mushrooms." 
The  real  body  of 
the  plant  is  the 
white  thread  -  like 
mycelium,  while 
the  "  mushroom  " 
part  seems  to  rep- 
resent a  great  num- 
ber of  sporophores 
organized  together 
to  form  a  single 
complex  spore- 
bearing  structure. 

The  mushroom 
23. 


Fig.  56.  A  common  Agariciis  :  A,  section  through  one 
side  of  pik'us,  showing  sections  of  the  pendent  gills; 
B.  section  of  a  gill  more  enlarged,  showing  the  cen- 
tral tissue,  and  the  broad  border  formed  by  the  ba- 
sidia :  C,  still  more  enlarged  section  of  one  side  of 
a  gill,  showing  the  club-shaped  basidia  standing  at 
right  angles  to  the  surface,  and  sending  out  a  pair 
of  small  branches,  each  of  which  bears  a  single  ba- 
sidiospore.— After  Sachs. 


w% 

jWl 

^HVv 

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^Bk:      ^1 

HH|| 

^ 

^K^^l 

^^^^1 

'il 

Ifc'^ 

^^m..-:M-  -■■  jsM 

^^^^^^^^^1 

ii\ 

V^\     s.^^1 

^Hf|H^^4^^ 

^^^^^^B 

i  ;1 

^v^|H 

^^K -;  '''■'    ^-^3^H 

m^^i 

ii 

i^^l 

c    o 


cc     <>7  "3 


5^ 


THALLOPIIYTES:  FUNGI 


71 


has  a  stalk-like  portion,  the  stij^e,  at  the  base  of  which  the 
slender  mycelial  threads  look  like  white  rootlets ;  and  an 
expanded,  umbrella-like  top  called  the  pileus.  From  the 
under  surface  of  the  pileus  there  hang  thin  radiating  plates, 
or  gills  (Fig.  55).  Each  gill  is  a  mass  of  interwoven  fila- 
ments (hyphae),  whose  tips  turn  toward  the  surface  and 
form  a  compact  layer  of  end  cells  (Fig.  56).     These  end 


Fig.  60.    A  bracket  fungus  (Polyporus)  growing  on  the  trunk  of  a  red  oak.- 
Caldwell. 


cells,  forming  the  surface  of  the  gill,  are  club-shaped,  and 
are  called  basidin.  From  the  broad  end  of  each  basidium 
two  or  four  delicate  branches  arise,  each  bearing  a  minute 
spore,  very  much  as  the  sporidia  appear  in  the  wheat  rust. 


12 


PLANT  STRUCTUEES 


These  spores,  called  basidiospores,  shower  down  from  the 
gills  when  ripe,  germinate,  and  produce  new  mycelia.  The 
peculiar  cell  called  the  basidium  gives  name  to  the  group 
Basidiomycetes. 

50.  Other  forms. — Mushrooms  display  a  great  variety  of 
form  and  coloration,  many  of  them  being  very  attractive 


Fig.  61. 


A  toadstool  of  the  bracket  form  which  has  grown  about  blades  of  grass 
without  interfering  with  their  activity.— Caldwell. 


(Figs.  57,  58,  59).  The  "  pore-fungi  "  have  pore-like  depres- 
sions for  their  spores,  instead  of  gills,  as  in  the  very  com- 
mon "bracket-fungus"  {Polyporus),  which  forms  hard 
shell-like  outgrowths  on  tree-trunks  and  stumps  (Figs.  60, 


Fig.  62.    The  common  edible  Boletus  (B.edu-  Fig.  63.    Another  edible  Boletus  {B.  .ilro- 

lis),   in  which  the  gills  are  replaced  by  bilaceiis).— After  Gibson. 

pores.— After  Gibson. 


Fi<i.  64.    The  common  edible  "  coral  fun- 
gus "  (CViU'««a).— After  Gibson. 


Fk;.  6."  ////(///'///* /'//(//((/wwi,  in  which  gills 
arc  rijUuccd  hy  .vpiuous  processes  ;  edi- 
ble.— After  Gibson. 


74 


PLANT   STKUCTUKES 


61),  and  the  muslirooxn-like  Boleti  (Figs.  G2,  63).  The 
"  ear-fungi "  form  gelatinous,  dark-brovn,  shell-shaped 
masses,  and  the  "  coral  fungi "  resemble  branching  corals 
(Fig.    64).      The    Hydnum   forms   have   spinous   jjrocesses 

instead  of  gills  (Fig. 
65).  The  puffballs  or- 
ganize globular  bodies 
(Fig.  66),  within  which 
the  spores  develop,  and 
are  not  liberated  until 
ripe ;  and  Avith  them 
belong  also  the  "bird's 
nest  fungus,"  the  "earth 
star,"  the  ill-smelling 
"  stink-horn,"  etc. 

OTHER  THALLOPHYTES 
WITHOUT  CHLOEOPHYLL 


5 1 .   Slime  -  moulds.  — 

These  perplexing  forms, 
named  Mijxomycetes,  do 
not  seem  to  be  related 
to  any  group  of  jilants, 


Fig.  66.    Piiffballs,  in  which  the  basidia  and 
spores  are  inclosed ;  edible. — After  Gibson. 


and  it  is  a  question 
whether  they  are  to  be  regarded  as  plants  or  animals.  The 
working  body  is  a  mass  of  naked  protoplasm  called  a  ^;/fts- 
modinm,  suggesting  the  term  "slime,"  and  slips  along  like 
a  gigantic  amoeba.  They  are  common  in  forests,  upon 
black  soil,  fallen  leaves,  and  decaying  logs,  the  slimy  yel- 
low or  orange  masses  ranging  from  the  size  of  a  pinhead 
to  as  large  as  a  man's  hand.  They  are  saprophytic,  and 
are  said  to  engulf  food  as  do  the  amoebas.  So  suggestive 
of  certain  low  animals  is  this  body  and  food  habit  that 
slime-moulds  have  also  been  called  Mycetozoa  or  "  fungus- 
animals." 


TIIALLOPIIYTES:  FUNGI 


75 


In  certain  conditions,  however,  these  slimy  bodies  come 
"to  rest  and  organize  most  elaborate  and  often  very  beau- 
tiful   sporangia,   full   of   spores    (Fig.    07).      These  varied 
and   easily  preserved   sporangia  are   used    to   classify  the 


Fig.  67.  Three  common  slime  moulds  (Myxomycetes)  on  decaying  wood:  to  the 
left  above,  groups  of  ihe  sessile  sporangia  of  Trichia  ;  to  the  right  above,  a  group 
of  the  stalked  sporangia  of  Stemonitis,  with  remnant  of  old  Plasmodium  at  base; 
below,  groups  of  sporangia  of  Uetniarajria,  with  a  Plasmodium  mass  at  upper 
left  hand. — Goldbekueb. 


forms.  Slime-moulds,  or  "  slime-fungi,"  therefore,  seem 
to  have  animal-like  bodies  which  produce  plant-like  spo- 
rangia. 

52.  Bacteria. — These  are  the  "  Fission-Fungi,"  or  Schizo- 
mycetes,  and  are  popularly  known  as  "  bacteria,"  "  baci Ji," 
"  microbes,"  "  germs,"  etc.  They  are  so  important  and  pe- 
culiar in  their  life  habits  that  their  study  has  developed  a 
special  branch  of  botany,  known  as  "  Bacteriology."  In 
many  ways  they  resemble  the  Cyanophycese,  or  "  Fission- 
Algae,"  so  closely  that  they  are  often  associated  with  them 
in  classification  (see  §  21). 


Fig.  68.  A  group  of  Bacteria,  the  bodies  being  black,  and  bearing  motile  cilia  in 
various  ways.  .4,  the  two  to  the  left  the  common  hay  Bacillus  (B.  subtilis),  the 
one  to  the  right  a  Spirillum  ;  B,  a  Coccus  form  (Planococcus);  C,  I),  £,  species  of 
Pseudonionas  :  F,  G,  species  of  Bacillus,  i^  being  that  of  typhoid  fever;  E,  Micro- 
spira ;  J,  K,  L,  M,  species  of  Spirillum.— After  Engler  and  Prantl. 


THALLOFHYTES:  FUNGI  77 

They  are  the  smallest  known  living  organisms,  the  one- 
celled  form  which  develops  on  cooked  potatoes,  bread,  milk, 
meat,  etc.,  forming  a  blood-red  stain,  having  a  diameter  of 
but  0.0005  mm.  (jo^o-o  ^^•)-  I'^ej  are  of  various  forms 
(Fig.  68),  as  Coccus  forms,  single  spherical  cells ;  Bacterium 
forms,  short  rod-shaped  cells ;  Bacillus  forms,  longer  rod- 
shaped  cells ;  Leptothrix  forms,  simple  filaments ;  Spirillum 
forms,  spiral  filaments,  etc. 

They  multiply  by  cell  division  with  wonderful  rapidity, 
and  also  form  resting  spores  for  preservation  and  distri- 
bution. They  occur  everywhere — in  the  air,  in  the  water, 
in  the  soil,  in  the  bodies  of  plants  and  animals ;  many  of 
them  harmless,  many  of  them  useful,  many  of  them  dan- 
gerous. 

They  are  intimately  concerned  with  fermentation  and 
decay,  inducing  such  changes  as  the  souring  of  fruit  Juices, 
milk,  etc.,  and  the  development  of  pus  in  wounds.  What 
is  called  antiseptic  surgery  is  the  use  of  various  means  to 
exclude  bacteria  and  so  prevent  inflammation  and  decay. 

The  pathogenic  forms — that  is,  those  which  induce  dis- 
eases of  plants  and  animals — are  of  great  importance,  and 
means  of  making  them  harmless  or  destroying  them  are 
being  searched  for  constantly.  They  are  the  causes  of  such 
diseases  as  pear-blight  and  peach-yellows  among  plants,  and 
such  human  diseajses  as  tuberculosis,  cholera,  diphtheria, 
typhoid  fever,  etc. 

LICHENS 

53.  General  character.  —  Lichens  are  abundant  every- 
where, forming  various  colored  splotches  on  tree-trunks, 
rocks,  old  boards,  etc.,  and  growing  also  upon  the  ground 
(Figs.  69,  70,  71).  They  have  a  general  greenish-gray  color, 
but  brighter  colors  may  also  be  observed. 

The  great  interest  connected  with  Lichens  is  that  they  are 
not  single  plants,  but  each  Lichen  is  formed  of  a  fungus  and 
an  alga,  living  together  so  intimately  as  to  appear  like  a  single 


TIIALLOPIIYTES:  FUNGI 


79 


plant.    In  other  words,  a  Lichen  is  not  an  individual,  but  a 
firm  of  two  individuals  very  unlike  each  other.     This  habit 


Fig.  70.    A  common  lichen  {Physcia)  growing  on  bark,  sliowing  the  spreading  thallus 
and  the  numerons  dark  disks  (apothecia)  bearing  the  asci. — Ooldberger. 

of  living  together  has  been  called  symbiosis^  and  the  indi- 
viduals entering  into  this  relation  are  called  symUonts. 


Fio.  71.    A  common  foliose  lichen  (Panndia)  growing  upon  a  board,  and  showing 
apothecia.— GoLDBEKGER. 


80 


PLANT   STRDCTUKES 


If  a  Lichen  be  sectioned,  the  relation  between  the  sym- 
bionts  will  be  seen  (Fig.  72).  The  fungus  makes  the  bulk 
of  the  body  with  its  interwoven  mycelial  threads,  in  the 
meshes  of  which  lie  the  Alg«,  sometimes  scattered,  some- 


FiG.  72.    Section  through  thalhis  of  a  lichen  {Sticta),  showing  holdfasts  (r),  lower  (m) 
and  upper  (o)  surfaces,  fungus  hj'phs  (m),  and  enmeshed  algie  (g-).— After  Sachs. 


times  massed.  It  is  these  enmeshed  Algae,  showing  through 
the  transparent  mycelium,  that  give  the  greenish  tint  to 
the  Lichen. 

In  the  case  of  Lichens  the  symbionts  are  thought  by 
some  to  be  mutually  helpful,  the  alga  manufacturing  food 
for  the  fungus,  and  the  fungus  providing  protection  and 
water  containing  food  materials  for  the  alga.  Others  do  not 
recognize  any  special  benefit  to  the  alga,  and  see  in  a  Lichen 
simply  a  parasitic  fungus  living  on  the  products  of  an  alga. 
In  any  event  the  Algae  are  not  destroyed  but  seem  to  thrive. 
It  is  discovered  that  the  alga  symbiont  can  live  quite  inde- 


THALLOrilYTES:   FUNGI  81 

pendently  of  the  fungus.  In  fact,  the  enmeshed  Algae  are 
often  recognized  as  identical  with  forms  living  independ- 
ently, those  thus  used  being  various  Blue-green,  Protococ- 
cus,  and  Conferva  forms  (see  p.  87). 

On  the  other  hand,  the  fungus  symbiont  has  become 
quite  dependent  upon  the  alga,  and  its  germinating  spores 
do  not  develop  far  unless  the  young  mycelium  can  lay  hold 
of  suitable  Algss.  At  certain  times  cup-like  or  disk-like 
bodies  appear  on  the  surface  of  the  lichen  thallus,  with 
brown,  or  black,  or  more  brightly-colored  lining  (Figs.  70, 
71).  These  bodies  are  the  opothecia,  and  a  section  through 
them  shows  that  the  colored  lining  is  largely  made  up  of 
delicate  sacs  containing  spores  (Figs.  73,  74).  These  sacs 
are  evidently  asci,  the  apothecia  correspond  to  ascocarps, 
and  the  Lichen  fungus  proves  to  be  an  Ascomycete. 

f'-V, 


-Z^^JpS^.:?  .,  ^--V4v.^*\ 


V  ^'v,  «•  V 


'"^^^.  ,yry^^ 


V 


m 

Fig.  T3.  Section  through  an  apothecinm  of  Anaptychia,  showing  stalk  of  the  cup 
(in),  masses  of  algal  cells  (<?),  outer  margin  of  cup  (;■),  overlapping  edge  {t,  t),  layer 
of  asci  (A),  and  massing  of  hyphfe  beneath  asci  (y).— After  Sachs. 

Certain  Ascomycetes,  therefore,  have  learned  to  use  cer- 
tain Algge  in  this  peculiar  way,  and  a  Lichen  is  the  result. 
Some  Basidiomycetes  have  also  learned  the  same  habit,  and 
form  Lichens. 

Various  forms  of  Lichen  bodies  can  be  distinguished  as 
follows  :  (1)  Crustaceous  Lichens,  in  which  the  thallus  resem- 


82 


PLANT   STEUCTUKES 


bles  an  incrustation  upon  its  substratum  of  rock,  soil,  etc. ; 
(2)  Foliose  LicJtens,  with  flattened,  leaf-like,  lobed  bodies,  at- 


PiG.  74.  Much  enlarged  section  of  a  portion  of  the  apothecium  of  Anaptychia,  show- 
ing the  fungus  mycelium  (m),  which  is  massed  above  iy),  just  beneath  the  layer  of 
asci  {1,  2,  3,  4),  in  which  spores  in  various  stages  of  development  are  shown.— 
After  Sachs. 


tached  only  at  the  middle  or  irregularly  to  the  substratum ; 
(3)  Fruticose  Licliens,  with  filamentous  bodies  branching 
like  shrubs,  either  erect,  pendulous,  or  prostrate. 


CHAPTEE   VI 

THE    FOOD    OF    PLANTS 

54.  Introductory. — All  plants  use  the  same  kind  of  food, 
but  the  Algsd  and  Fungi  suggest  that  they  may  have  very 
different  ways  of  obtaining  it.  The  Algse  can  manufacture 
food  from  raw  material,  while  the  Fungi  must  obtain  it 
already  manufactured.  Between  these  two  extreme  condi- 
tions there  are  plants  which  can  manufacture  food,  and  at 
the  same  time  have  formed  the  habit  of  supplementing  this 
by  obtaining  elsewhere  more  or  less  manufactured  food. 
Besides  this,  there  are  plants  which  have  learned  to  work 
together  in  the  matter  of  food  supply,  entering  into  a  con- 
dition of  symbiosis,  as  described  under  the  Lichens.  These 
various  habits  will  be  presented  here  briefly. 

55.  Green  plants. — The  presence  of  chlorophyll  enables 
plants  to  utilize  carbon  dioxide  (COg),  a  gas  present  in  the 
atmosphere  and  dissolved  in  waters,  and  one  of  the  waste 
products  given  off  in  the  respiration  of  all  living  organisms. 
This  gas  is  absorbed  by  green  plants,  its  constituent  ele- 
ments, carbon  and  oxygen,  are  dissociated,  and  with  the  ele- 
ments obtained  from  absorbed  water  (HgO)  are  recombined  to 
form  a  carbohydrate  (sugar,  starch,  etc.),  which  is  an  organ- 
ized food.  With  this  as  a  basis  other  foods  are  formed, 
and  so  the  plant  can  live  without  help  from  any  other 
organism. 

This  process  of  utilizing  carbon  dioxide  in  the  formation 
of  food  is  not  only  a  wonderful  one,  but  also  very  important. 
It  is  wonderful,  because  carbon  dioxide  and  water,  both  of 
them  very  refractory  svibstances,  are  broken  up  at  ordinary 

83 


84:  PLANT  STRUCTUEES 

temperatures  and  without  any  special  display  of  energy.  It 
is  important,  because  the  food  of  all  plants  and  animals  de- 
pends upon  it,  as  it  is  the  only  known  process  by  which  inor- 
ganic material  can  be  organized. 

The  process  is  called  pliotosyntliesis^  or  plioto^yntax^ 
words  indicating  that  the  presence  of  light  is  necessary. 
The  mechanism  on  the  part  of  the  plant  is  the  chloroplast, 
which  when  exposed  to  light  is  able  to  do  this  work.  The 
process  is  often  called  "  carbon  assimilation,"  "  chlorophyll 
assimilation,"  "  fixation  of  carbon,"  etc.  It  should  be  noted 
that  it  is  not  the  chlorophyll  which  does  the  work,  but  the 
protoplasmic  plastid  stained  green  by  the  chlorophyll.  The 
chlorophyll  manipulates  the  liglit  in  some  way  so  that  the 
plastid  may  obtain  from  it  the  energy  needed  for  the  work. 
Further  details  concerning  it  may  be  obtained  by  reading 
§  112  of  Plant  Belations. 

It  is  evident  that  green  plants  must  expose  their  chloro- 
phyll to  the  light.  For  this  reason  the  Algge  can  not  live 
in  deep  waters  or  in  dark  places.  In  the  case  of  the  large 
marine  kelps,  although  they  may  be  anchored  in  considera- 
ble depth  of  water,  their  working  bodies  are  floated  up 
toward  the  light  by  air-bladders.  In  the  case  of  higher 
plants,  specially  organized  chlorophyll-bearing  organs,  the 
foliage  leaves,  are  developed. 

56.  Saprophytes. — Only  cells  containing  chloroplasts  can 
live  independently.  In  the  higher  plants,  where  bodies  be- 
come large,  many  living  cells  are  shut  away  from  the  light, 
and  must  depend  upon  the  more  superficial  green  cells  for 
their  food  supply.  The  habit  of  cells  depending  upon  one 
another  for  food,  therefore,  is  a  very  common  one. 

When  none  of  the  cells  of  the  plant  body  contain  chloro- 
phyll, the  whole  plant  becomes  dependent,  and  must  live  as 
a  saprophyte  or  a  parasite.  In  the  case  of  saprophytes  dead 
bodies  or  body  products  are  attacked,  and  sooner  or  later  all 
organic  matter  is  attacked  and  decomposed  by  them.  The 
decomposition  is  a  result  of  the  nutritive  processes  of  plants 


THE   FOOD   OF  PLANTS  35 

without  chlorophyll,  and  were  it  not  for  them  "the  whole 
surface  of  the  earth  would  be  covered  with  a  thick  deposit 
of  the  animal  and  plant  remains  of  the  past  thousands  of 
years." 

The  green  plants,  therefore,  are  the  manufacturers  of 
organic  material,  producing  far  more  than  they  can  use, 
while  the  plants  without  chlorophyll  are  the  destroyers  of 
organic  material.  The  chief  destroyers  are  the  Bacteria 
and  ordinary  Fungi,  but  some  of  the  higher  plants  have 
also  adopted  this  method  of  obtaining  food.  Many  ordinary 
green  plants  have  the  saprophytic  habit  of  absorbing  organic 
material  from  rich  humus  soil ;  and  some  plants  (as  broom 
rapes)  are  parasitic,  attaching  their  subterranean  parts  to 
those  of  other  plants,  becoming  what  are  called  "  root  para- 
sites." In  cases  of  mycorhiza  (see  p.  87),  which  are  now 
thought  to  include  great  numbers  of  green  plants,  it  is  sup- 
posed that  some  organic  material  is  brought  in  by  the  fungus. 

57.  Parasites. — Certain  plants  without  chlorophyll  are 
not  content  to  obtain  organic  material  from  dead  bodies, 
but  attack  living  ones.  As  in  the  case  of  saprophytes,  the 
vast  majority  of  plants  which  have  formed  this  habit  are 
Bacteria  and  ordinary  Fungi.  Parasites  are  not  only  modi- 
fied in  structure  in  consequence  of  the  absence  of  chloro- 
phyll, but  they  have  developed  means  of  penetrating  their 
hosts.  Many  of  them  have  also  cultivated  a  very  selective 
habit,  restricting  themselves  to  certain  plants  or  animals,  or 
even  to  certain  organs. 

The  parasitic  habit  has  also  been  developed  by  some  of 
the  higher  plants,  sometimes  completely,  sometimes  par- 
tially. Dodder,  for  example,  is  completely  parasitic  at 
maturity  (Fig.  75),  while  mistletoe  is  only  partially  so, 
doing  chlorophyll  work  and  also  absorbing  from  the  tree 
into  which  it  has  sent  its  haustoria. 

That  saprophytism  and  parasitism  are  both  habits  grad- 
ually acquired  is  inferred  from  the  number  of  green  plants 
which  have  developed  them  more  or  less,  as  a  supplement  to 
24 


86 


PLANT   STEUCTURES 


tlie  food  which  they  manufacture.  The  less  chlorophyll  is 
used  the  less  is  it  developed,  and  a  green  plant  which  is 
obtaining  the  larger  amount  of  its  food  in  a  saprophytic 

or  parasitic  way  is 
on  the  way  to  losing 
all  of  its  chlorophyll 
and  becoming  a  com- 
plete saprophyte  or 
parasite. 

Certain  of  the  low- 
er Algae  are  in  the 
habit  of  living  in  the 
body  cavities  of  high- 
er plants,  finding  in 
such  situations  the 
moisture  and  protec- 
tion which  they  need. 
They  may  thus  have 
brought  within  their 
reach  some  of  the 
organic  products  of 
the  higher  plant.  If 
they  can  use  some  of 
these,  as  is  very  like- 
ly, a  partially  para- 
sitic habit  is  begun, 
which  may  lead  to 
loss  of  chlorophyll 
and  complete  para- 
sitism. 

58.    Symbionts.  — 
Symh iosis    means 
"living       together," 
and  two  organisms  thus  related  are  called  syinhmits.     In 
its  broadest  sense  symbiosis  includes  any  sort  of  depend- 
ence between  living  organisms,  from  the  vine  and  the  tree 


\ 


Fig.  75.  A  dodder  plant  parasitic  on  a  willow  twig. 
The  leafless  dodder  twines  about  the  willow,  and 
sends  out  sucking  processes  which  penetrate  and 
absorb. — After  Stbasburger. 


THE   FOOD    OF  PLANTS  87 

upon  which  it  climbs,  to  the  alga  and  fungus  so  intimately 
associated  in  a  Lichen  as  to  seem  a  single  plant.  In  a  nar- 
rower sense  it  includes  only  cases  in  which  there  is  an  inti- 
mate organic  relation  between  the  symbionts.  This  would 
include  parasitism,  the  parasite  and  host  being  the  sym- 
bionts, and  the  organic  relation  certainly  being  intimate. 
In  a  still  narrower  sense  symbiosis  includes  only  those  cases 
in  which  the  symbionts  are  mutually  helpful.  This  fact, 
however,  is  very  diflBcult  to  determine,  and  opinions  vary 
widely  as  to  the  mutual  advantage  in  certain  cases.  How- 
ever large  a  set  of  phenomena  may  be  included  under  the 
term  symbiosis,  we  use  it  here  in  this  narrowest  sense, 
which  is  often  distinguished  as  inutuaUsm. 

(1)  Lichens. — A  lichen  is  a  complex  made  up  of  a  fun- 
gus and  an  alga  living  together.  It  is  certain  that  the  fun- 
gus cannot  live  without  the  alga,  but  the  alga  can  live 
without  the  fungus.  Hence  it  seems  plain  that  this  rela- 
tion is  not  one  of  mutual  helpfulness,  but  that  the  fungus 
is  living  upon  the  alga,  as  any  other  parasite  lives  upon  its 
host  (see  §  194). 

(2)  Mijcorhiza. — The  name  means  "root-fungus,"  and 
refers  to  an  association  which  exists  between  certain  Fungi 
of  the  soil  and  roots  of  higher  plants.  It  was  formerly 
thought  that  mycorhiza  occurred  only  in  connection  with 
a  limited  number  of  higher  plants,  such  as  orchids,  heaths, 
oaks,  etc.,  but  more  recent  study  indicates  that  probably 
the  large  majority  of  vascular  plants  (that  is,  plants  with 
true  roots)  possess  it,  the  water  plants  being  excepted  (Figs. 
149,  150).  It  has  been  found  that  the  humus  soil  of  forests 
is  in  large  part  "  a  living  mass  of  innumerable  filamentous 
fungi."  It  is  clearly  of  advantage  to  roots  to  relate  them- 
selves to  this  great  network  of  filaments,  which  are  already 
in  the  best  relations  for  absorption,  and  those  plants  which 
are  unable  to  do  this  are  at  a  disadvantage  in  the  competi- 
tion for  the  nutrient  materials  of  the  forest  soil.  It  is 
doubtful  whether  many  vascular  green  plants  can  absorb 


^ 


Fig.  76.  Mycorhiza :  to  the  left  is  the  tip  of  a  rootlet  of  beech  enmeshed  by  the 
fungus;  A,  diagram  of  longitudinal  section  of  an  orchid  root,  showing  the  cells 
of  the  cortex  (;;)  filled  with  hyphse;  B,  part  of  longitudinal  section  of  orchid  root 
much  enlarged,  showing  epidermis  («),  outermost  cells  of  the  cortex  {p)  filled  with 
hyphal  threads,  which  are  sending  branches  into  the  adjacent  cortical  cells  (a,  i). 
—After  Frank. 


Fig.  77.  Mycorhiza :  A^  rootlets  of  white  poplar  forming  mycorhiza  ;  B,  enlarged 
section  of  single  rootlets,  showing  the  hyphae  penetrating  the  cells.— After 
ELebner. 


THE   FOOD    OF   PLANTS 


89 


enough  for  their  needs  from  the  soil  without  this  assistance, 
and,  if  so,  the  fungus  becomes  of  vital  importance  in  the 
nutrition  of  such  plants.  In  the  case  of  some  of  these 
plants  it  seems  that  the  soil  fungus  is  not  merely  passing 
into  their  bodies  the  soil  water  with  its  dissolved  salts,  but 
is  contributing  to  them  organized  food,  thus  diminishing 
the  amount  of  necessary  food  manu- 
facture. The  delicate  branching  fila- 
ments (hyphse)  of  the  fungus  wrap 
the  rootlets  with  a  mesh  of  hyphae 
and  penetrate  into  the  cells,  and  it 
is  evident  that  the  fungus  obtains 
food  from  the  rootlet  as  a  parasite. 

(3)  Boot-tubercles. — On  the  roots 
of  many  legume  plants,  as  clovers, 
peas,  beans,  etc.,  little  wart -like 
outgrowths  are  frequently  found, 
known  as  "  root-tubercles "  (Fig. 
78).  It  is  found  that  these  tuber- 
cles are  caused  by  certain  Bacteria, 
which  penetrate  the  roots  and  in- 
duce these  excrescent  growths.  The 
tubercles  are  found  to  swarm  with 
Bacteria,  which  are  doubtless  ob- 
taining food  from  the  roots  of  the 
host.  At  the  same  time,  these  Bac- 
teria have  the  peculiar  power  of 
laying  hold  of  the  free  nitrogen  of 
the  air  circulating  in  the  soil,  and 
of  supplying  it  to  the  host  plant 
in  some  usable  form.  Ordinarily 
plants  can  not   use  free   nitrogen, 

although  it  occurs  in  the  air  in  such  abundance,  and  this 
power  of  these  soil  Bacteria  is  peculiarly  interesthig. 

This  habit  of  clover  and  its  allies  explains  why  they  are 
useful  in  what  is  called  "  restoring  the  soil."     After  ordi- 


FiG.  78.     Root-tubercles  on 
Vicia  Faba. —After  Noll. 


90 


PLANT   STRUCTURES 


nary  crops  have  exhausted  the  soil  of  its  nitrogen-contain- 
ing salts,  and  it  has  become  comparatively  sterile,  clover  is 
able  to  grow  by  obtaining  nitrogen  from  the  air  through  the 
root-tubercles.  If  the  crop  of  clover  be  "  plowed  under," 
nitrogen-containing  materials  which  the  clover  has  organ- 
ized will  be  contributed  to  the  soil,  which  is  thus  restored 
to  a  condition  which  will  support  the  ordinary  crops  again. 
This  indicates  the  significance  of  a  very  ordinary  "  rotation 
of  crops." 

(4)  Ant-plants,  etc. — In  symbiosis  one  of  the  symbionts 
may  be  an  animal.  Certain  fresh-water  polyps  and  sponges 
become  green  on  account  of  Algge  which  they  harbor  with- 
in their  bodies  (Fig.  79).  Like 
the  Lichen-fungus,  these  animals 
are  benefited  by  the  presence  of 
the  Algae,  which  in  turn  find  a 
congenial  situation  for  living. 
By  some  this  would  also  be  re- 
garded as  a  case  of  helotism, 
the  animal  enslaving  the  alga. 

Very  definite  arrangements 
are  made  by  certain  plants  for 
harboring  ants,  which  in  turn 
guard  them  against  the  attack 
of  leaf-cutting  insects  and  oth- 
er foes.  These  plants  are  called 
Myrmecophytes,  which  means 
"  ant-plants,"  or  rnyrmecophilous 
plants,  which  means  "plants  loving  ants."  These  plants 
are  mainly  in  the  tropics,  and  in  stem  cavities,  in  hollow 
thorns,  or  elsewhere,  they  provide  dwelling  places  for  tribes 
of  warlike  ants  (Fig.  80).  In  addition  to  these  dwelling 
places  they  provide  special  kinds  of  food  for  the  ants. 

(5)  Flowers  and  insects. — A  very  interesting  and  impor- 
tant case  of  symbiosis  is  that  existing  between  flowers  and 
insects.     The  flowers  furnish  food  to  the  insects,  and  the 


Fig.  79.  A  fresh-water  polyp  {Hy- 
dra) attached  to  a  twig  and  con- 
taining algoe  (C),  which  may  be 
seen  through  the  transparent 
body  wall  (i?).— Goldbergek. 


THE  FOOD    OF   PLANTS 


91 


latter  are  used  by  the  flowers  as  agents  of  pollination.     An 
account  of  this  relationship  is  deferred  until  seed-plants  are 


Fig.  80.    An  ant  plant  {ITydnophytum)  from  South  Java,  in  which  an  excrescent 
growth  provides  a  habitation  for  ants.— After  Schimpek. 

considered,  or  it  may  be  found,  with  illustrations,  in  Plant 
Relations^  Chapter  YII. 


92  PLANT   STEDCTUKES 

59.  Carnivorous  plants. — Certain  green  plants,  growing 
in  situations  poor  in  nitrogen-containing  salts,  have  learned 
to  supplement  the  proteids  which  they  manufacture  by  cap- 
turing and  digesting  insects.  The  various  devices  employed 
for  securing  insects  have  excited  great  interest,  since  they 
do  not  seem  to  be  associated  with  the  ordinary  idea  of  plant 
activities.  Prominent  among  these  forms  are  the  bladder- 
worts,  pitcher-plants,  sundews,  Venus's  fly-trap,  etc.  For 
further  account  and  illustrations  of  these  plants  see  Plant 
Relations^  §  119« 


CHAPTER  VII 

BRYOPHYTES  (MOSS  PLANTS) 

60.  Summary  from  Thallophytes.— Before  considering  the 
second  great  division  of  plants  it  is  well  to  recall  the  most 
important  facts  connected  with  the  Thallophytes,  those 
things  which  may  be  regarded  as  the  contribution  of  the 
Thallophytes  to  the  evolution  of  the  plant  kingdom,  and 
which  are  in  the  background  when  one  enters  the  region  of 
the  Bryophytes. 

(1)  Increasing  complexity  of  the  5o6??/.— Beginning  with 
single  isolated  cells,  the  plant  body  attains  considerable 
complexity,  in  the  form  of  simple  or  branching  filaments, 
cell-plates,  and  cell-masses. 

(2)  Appeanmce  of  spores.— The  setting  apart  of  repro- 
ductive cells,  known  as  spores,  as  distinct  from  nutritive 
cells,  and  of  reproductive  organs  to  organize  these  spores, 
represents  the  first  important  differentiation  of  the  plant 
body  into  nutritive  and  reproductive  regions. 

(3)  Differentiation  of  spores.— After  the  introduction  of 
spores  they  become  different  in  their  mode  of  origin,  but 
not  in  their  power.  The  asexual  spore,  ordinarily  formed 
by  cell  division,  is  followed  by  the  appearance  of  the  sexual 
spore,  formed  by  cell  union,  the  .act  of  cell  union  being 
known  as  the  sexual  process. 

(4)  Differentiation  of  gametes.— At  the  first  appearance 
of  sex  the  sexual  cells  or  gametes  are  alike,  but  after- 
ward they  become  different  in  size  and  activity,  the  large 
passive  one  being  called  the  egg,  the  small  active  one  the 

yd 


Q4  PLANT   STRUCTURES 

sperm,  the  organs  producing  the  two  being  known  as  oogo- 
nium and  antheridium  respectively. 

(5)  Algm  the  main  line. — The  Algfe,  aquatic  in  liabit, 
appear  to  be  the  Thallophytes  which  lead  to  the  Bryophytes 
and  higher  groups,  the  Fungi  being  regarded  as  their  de- 
generate descendants  ;  and  among  the  Algae  the  Chloro- 
phyceae  seem  to  be  most  probable  ancestors  of  higher  forms. 
It  should  be  remembered  that  among  these  Green  Algaj  the 
ciliated  swimming  spore  (zoospore)  is  the  characteristic 
asexual  spore,  and  the  sexual  spore  (zygote  or  oospore)  is 
the  resting  stage  of  the  plant,  to  carry  it  over  from  one 
growing  season  to  the  next. 

61.  General  characters  of  Bryophytes. — The  name  given 
to  the  group  means  "  moss  plants,"  and  the  Mosses  may  be 
regarded  as  the  most  representative  forms.  Associated 
with  them  in  the  group,  however,  are  the  Liverworts,  and 
these  two  groups  are  plainly  distinguished  from  the  Thallo- 
phytes below,  and  from  the  Pteridophytes  above.  Starting 
with  the  structures  that  the  Algae  have  worked  out,  the 
Bryophytes  modify  them  still  further,  and  make  their  own 
contributions  to  the  evolution  of  the  plant  kingdom,  so 
that  Bryophytes  become  much  more  complex  than  Thallo- 
phytes. 

62.  Alternation  of  generations. — Probably  the  most  im- 
portant fact  connected  with  the  Bryophytes  is  the  distinct 
alternation  of  generations  which  they  exhibit.  So  impor- 
tant is  this  fact  in  connection  with  the  development  of  the 
plant  kingdom  that  its  general  nature  must  be  clearly  under- 
stood. Probably  the  clearest  definition  may  be  obtained  by 
tracing  in  bare  outline  the  life  history  of  an  ordinary  moss. 

Beginning  with  the  asexual  spore,  which  is  not  ciliated, 
as  there  is  no  water  in  which  it  can  swim,  we  may  imagine 
that  it  has  been  carried  by  the  wind  to  some  spot  suitable 
for  its  germination.  It  develops  a  branching  filamentous 
growth  which  resembles  some  of  the  Conferva  forms  among 
the  Green  Algae  (Fig.  81).     It  is  prostrate,  and  is  a  regu- 


BRYOPIIYTES 


95 


lar  thallus  body,  not  at  all  resembling  the  ''moss  plant" 
of  ordinary  observation,  and  is  not  noticed  by  those  una- 
ware of  its  existence. 

Presently  one  or  more  buds  appear  on  the  sides  of  this 
alga-like  body  (Fig.  81,  h).     A  bud  develops  into  an  erect 


Fig.  81.  Protonema  of  mo?s:  A,  very  young  protonema,  showing  spore  (-S")  which 
has  germinated  it;  B',  older  protonema,  showing  branching  habit,  remains  of 
spore  (s),  rhizoids  (?•).  and  buds  (6)  of  leafy  branches  (gametophores).— After 
MiJLLER  and  Thuroau. 


stalk  upon  which  are  numerous  small  leaves  (Figs.  82, 103). 
This  leafy  stalk  is  the  "moss  plant"  of  ordinary  observa- 
tion, and  it  will  be  noticed  that  it  is  simply  an  erect  leafy 
branch  from  the  prostrate  alga-like  body. 

At  the  top  of  this  leafy  branch  sex-organs  appear,  cor- 
responding to  the  antheridia  and  oogonia  of  the  Algae,  and 
within  them  there  are  sperms  and  eggs.  A  sperm  and  eg^ 
fuse  and  an  oospore  is  formed  at  the  summit  of  the  leafy 
branch. 

The  oospore  is  not  a  resting  spore,  but  germinates  im- 
mediately, forming  a  structure  entirely  unlike  the  moss 


96 


PLANT   STEUCTURES 


,rh 


Fig.  82.  A  common  moss 
{Polytrichum  cormnime), 
showing  the  leafy  gameto- 
phore  with  rhizoids  (rh), 
and  two  sporophytes  (sporo- 
gonia),  with  seta  (s),  calyp- 
tra  (c),  and  operculum  (d), 
the  calyptra  having  been  re- 
moved.— After  ScHENCK. 


plant  from  which  it  came.  This  new 
leafless  body  consists  of  a  slender 
stalk  bearing  at  its  summit  an  urn- 
like case  in  which  are  developed  nu- 
merous asexual  spores  (Figs.  82, 107). 
This  whole  structure  is  often  called 
the  "spore  fruit,"  and  its  stalk  is 
imbedded  at  base  in  the  summit  of 
the  leafy  branch,  thus  obtaining  firm 
anchorage  and  absorbing  what  nour- 
ishment it  needs,  but  no  more  a  part 
of  the  leafy  branch  than  is  a  para- 
site a  part  of  the  host. 

When  the  asexual  spores,  pro- 
duced by  the  "  spore  fruit,"  germi- 
nate, they  reproduce  the  alga-like 
body  with  which  we  began,  and  the 
life  cycle  is  completed. 

In  examining  this  life  history,  it 
is  apparent  that  each  spore  produces 
a  different  structure.  The  asexual 
spore  produces  the  alga-like  body 
with  its  erect  leafy  branch,  while 
the  oospore  produces  the  "  spore 
fruit"  with  its  leafless  stalk  and 
spore  case.  These  two  structures, 
one  produced  by  the  asexual  spore, 
the  other  by  the  oospore,  appear  in 
alternating  succession,  and  this  is 
what  is  meant  by  aliernation  of  ge7i- 
erations. 

These  two  "generations"  differ 
strikingly  from  one  another  in  the 
spores  which  they  produce.  The 
generation  composed  of  alga -like 
body   and    erect    leafy  branch   pro- 


BRYOPIIYTES  97 

duces  only  sexual  spores  (oospores),  and  therefore  pro- 
duces sex  organs  and  gametes.  It  is  known,  therefore, 
as  the  gametophyte — that  is,  "the  gamete  plant." 

The  generation  which  consists  of  the  "spore  fruit" — 
that  is,  leafless  stalk  and  spore  case — produces  only  asexual 
spores,  and  is  called  the  sporoidliifte — that  is,  "  the  spore 
plant." 

Alternation  of  generations,  therefore,  means  the  alter- 
nation of  a  gametophyte  and  a  sporophyte  in  completing  a 
life  history.  Instead  of  having  the  same  body  produce  both 
asexual  and  sexual  spores,  as  in  most  of  the  Algae,  the  two 
kinds  of  spores  are  separated  upon  different  structures, 
known  as  "generations."  It  is  evident  that  the  gameto- 
phyte is  the  sexual  generation,  and  the  sporophyte  the 
asexual  one ;  and  it  should  be  kept  clearly  in  mind  that 
the  asexual  spore  always  produces  the  gametophyte,  and 
the  sexual  spore  the  sporophyte.  In  other  words,  each 
spore  produces  not  its  own  generation,  but  the  other  one. 

The  relation  between  the  two  alternating  generations 
may  be  indicated  clearly  by  the  following  formula,  in 
which  G  and  S  are  used  for  gametophyte  and  sporophyte 
respectively : 

G=8>o— S— 0— CT=:g>o— S— 0— G,  etc. 

The  formula  indicates  that  the  gametophyte  produces 
two  gametes  (sperm  and  Qgg),  which  fuse  to  form  an  oospore, 
which  produces  the  sporophyte,  which  produces  an  asexual 
spore,  Avhich  produces  a  gametophyte,  etc. 

That  alternation  of  generations  is  of  great  advantage  is 
evidenced  by  the  fact  that  it  appears  in  all  higher  plants. 
It  must  not  be  supposed  that  it  appears  first  in  the  Bryo- 
phytes,  for  its  beginnings  may  be  seen  among  the  Thallo- 
phytes.  The  Bryophytes,  however,  first  display  it  fully 
organized  and  without  exception.  Just  what  this  alterna- 
tion does  for  plants  may  not  be  fully  known,  but  one 
advantage  seems  prominent.  By  means  of  it  many  gameto- 
phytes  may  result  from  a  single  oospore  •  in  other  words. 


98  PLANT   STRDCTUKES 

it  multiplies  the  product  of  the  sexual  spore.  A  glance  at 
the  formula  given  above  shows  that  if  there  were  no  sporo- 
phyte  (S)  the  oospore  would  produce  but  one  gametophyte 
(G).  By  introducing  the  sporophyte,  however,  as  many 
gametophytes  may  result  from  a  single  oospore  as  there  are 
asexual  spores  produced  by  the  sporophyte,  which  usually 
produces  a  very  great  number. 

In  reference  to  the  sporophytes  and  gametophytes  of 
Bryophytes  two  peculiarities  may  be  mentioned  at  this 
point :  (1)  the  sporophyte  is  dependent  upon  the  gameto- 
phyte for  its  nourishment,  and  remains  attached  to  it ; 
(2)  the  gametophyte  is  the  special  chlorophyll -generation, 
and  hence  is  the  more  conspicuous.  It  follows  that,  in  a 
general  way,  the  sporophyte  of  the  Bryophytes  only  pro- 
duces spores,  while  the  gametophyte  both  produces  gametes 
and  does  chlorophyll  work. 

It  is  important  also  to  note  that  the  protected  resting 
stage  in  the  life  history  is  not  tlie  sexual  spore,  as  in  the 
Algse,  but  is  the  asexual  spore  in  connection  with  the 
sporophyte.  These  spores  have  a  protecting  wall,  are 
scattered,  and  may  remain  for  some  time  without  germi- 
nation. 

If  the  ordinary  terms  in  reference  to  Mosses  be  fitted 
to  the  facts  given  above,  it  is  evident  that  the  "moss 
plant "  is  the  leafy  branch  of  the  gametophyte  ;  that 
the  ''moss  fruit"  is  the  sporophyte;  and  that  the  alga- 
like part  of  the  gametophyte  has  escaped  attention  and 
a  popular  name. 

The  names  now  given  to  the  different  structures  which 
appear  in  this  life  history  are  as  follows  :  The  alga-like  part 
of  the  gametophyte  is  the  protonema,  the  leafy  branch  is 
the  gametopJiore  (''gamete-bearer  ") ;  the  whole  sporophyte 
is  the  sjyprogonium  (a  name  given  to  this  peculiar  leafless 
sporophyte  of  Bryophytes),  the  stalk-like  portion  is  the 
seta,  the  part  of  it  imbedded  in  the  gametophore  is  the 
foot,  and  the  urn-like  spore-case  is  the  capsule. 


BKYOPHYTES 


99 


63.  The  antheridium.— The  male  organ  of  the  Bryophjtes 
is  called  an  antheridium,  just  as  among  Thallophytes,  but 
it  has  a  very  different  structure.     In  general  among  the 


^lliib. 


Fig.  83.  Sex  organs  of  a  common  moss  (Funaria):  the  group  to  the  right  represents 
an  antheridium  (A)  discharging  from  its  apex  a  mass  of  sperm  mother  cells  (a),  a 
single  mother  cell  with  its  sperm  (6),  and  a  single  sperm  (c).  showing  body  and 
two  cilia;  the  group  to  the  left  represents  an  archegonial  cluster  at  summit  of 
stem  (.4).' showing  archegonia  (a),  and  paraphyses  and  leaf  sections  (b),  and  also  a 
single  archegoninm  (£).  with  venter  (b)  containing  egg  and  ventral  canal  cell,  and 
neck  (h)  containing  the  disorganizing  axial  row  (neck  canal  cells').— After  Sachs. 

Thallophytes  it  is  a  single  cell  (mother  cell),  and  may  be 
called  a  simple  antheridium,  but  in  the  Bryophytes  it  is  a 
many-celled  organ,  and  may  be  regarded  as  a  compound 
antheridium.    It  is  usually  a  stalked,  club-shaped,  or  oval  to 


100 


PLANT   STRUCTURES 


globular  body  (Figs.  83,  84,  103).  A  section  through  this 
body  shows  it  to  consist  of  a  single  layer  of  cells,  which 
forms  the  wall  of  the  antheridium,  and  within  this  a  com- 
pact mass  of  small  cubical  (square  in  section)  cells,  within 
each  one  of  which  there  is  formed  a  single  sperm  (Fig.  84). 
These  cubical  cells  are  evidently  moth- 
er cells,  and  to  distinguish  them  from 
others  they  are  called  sperm,  mother  cells. 
An  antheridium,  therefore,  aside  from 
its  stalk,  is  a  mass  of  sperm  mother 
cells  surrounded  by  a  wall  consisting 
of  one  layer  of  cells. 

The  sperm  is  a  very  small  cell  with 
two  long  cilia  (Fig.  83).  The  two 
parts  are  spoken  of  as  "body"  and 
cilia,  and  the  body  may  be  straight  or 
somewhat  curved.  These  small  bicili- 
ate  sperms  are  one  of  the  distinguish- 
ing marks  of  the  Bryophytes.  The 
existence  of  male  gametes  in  the  form 
of  ciliated  sperms  indicates  that  fertil- 
ization can  take  place  only  in  the  pres- 
ence of  water,  so  that  while  the  plant 
has  become  terrestrial,  and  its  asexual  spores  have  respond- 
ed to  the  new  conditions  and  are  no  longer  ciliated,  its 
sexual  process  is  conducted  as  among  the  Green  Algae.  It 
must  not  be  supposed,  however,  that  any  great  amount  of 
water  is  necessary  to  enable  sperms  to  swim,  even  a  film 
of  dew  often  answering  the  purpose. 

When  the  mature  antheridia  are  wet  they  are  opened 
at  the  apex  and  discharge  the  mother  cells  in  a  mass  (Figs. 
83,  105,  E),  the  walls  of  the  mother  cells  become  mucilagi- 
nous, and  the  sperms  escaping  swim  actively  about  and  are 
attracted  to  the  organ  containing  the  egg. 

64.  The  archegonium. — This  name  is  given  to  the  female 
sex  organ,  and  it  is  very  different  from  the  oogonium  of 


Fig.  84.  Antheridium  of 
a  liverwort  in  section, 
showing  single  layer 
of  wall  cells  surround- 
ing the  mass  of  moth- 
er cells. — After  Stras- 

BURGER. 


BRYOPIIYTES  101 

Thallophytes.  Instead  of  being  a  single  mother  cell,  it  is 
a  many-celled  structure,  shaped  like  a  flask  (Figs.  83,  98). 
The  neck  of  the  flask  is  more  or  less  elongated,  and  within 
the  bulbous  base  (venter)  the  single  egg  is  organized.  The 
archegonium,  made  up  of  neck  and  venter,  consists  mostly 
of  a  single  layer  of  cells.  This  hollow  flask  is  solid  at  first, 
there  being  a  central  vertical  row  of  cells  surrounded  by 
the  single  layer  just  referred  to.  All  of  the  cells  of  this 
axial  row,  except  the  lowest  one,  disorganize  and  leave  a 
passageway  down  through  the  neck.  The  lowest  one  of 
the  row,  which  lies  in  the  venter  of  the  archegonium,  or- 
ganizes the  egg.  In  this  way  there  is  formed  in  the  arche- 
gonium an  open  passageway  through  the  neck  to  the  egg 
lying  in  the  venter. 

To  this  neck  the  swimming  sperms  are  attracted,  enter 
and  pass  down  it,  one  of  them  fuses  with  the  egg,  and  this 
act  of  fertilization  results  in  an  oospore. 

Archegonia  and  antheridia  are  supposed  to  have  been 
derived  from  a  many-celled  gametangium,  such  as  occurs 
in  certain  Brown  Algae  (Fig.  18).  The  presence  of  the 
archegonia  is  one  strong  and  unvarying  distinction  between 
Thallophytes  and  Bryophytes.  Pteridophytes  also  have 
archegonia,  and  so  characteristic  an  organ  is  it  that  Bryo- 
phytes and  Pteridophytes  are  spoken  of  together  as  Arclie- 
goniatc)^. 

65.  Germination  of  the  oospore. — The  oospore  in  Bryo- 
phytes is  not  a  resting  spore,  but  germinates  immediately 
by  cell  division,  forming  the  sporophyte  embryo,  which 
presently  develops  into  the  mature  sporophyte  (Fig.  85,^). 
The  lower  part  of  the  embryo  develops  the  foot,  which  ob- 
tains a  firm  anchorage  in  the  gametophore  by  the  latter 
growing  up  around  it  (Fig.  85,  B,  C).  The  upper  part  of 
the  embryo  develops  the  seta  and  capsule.  As  the  embryo 
increases  in  size,  the  venter  of  the  archegonium  grows  also, 
forming  what  is  called  the  C(dy2)tra ;  and  in  true  Mosses 
the  embryo  presently  breaks  loose  the  calyptra  at  its  base 
25 


102 


PLANT  STRUCTURES 


and  carries  it  upward  perched  on  the  top  of  the  capsule  like 
a  loose  cap  or  hood  (Figs.  82,  c,  107),  which  sooner  or  later 

falls  ofE.  As  stated  be- 
fore, the  mature  struc- 
ture developed  from 
the  oospore  is  called  a 
sporogouium,  a  form  of 
sporophyte  peculiar  to 
the  Bryophytes. 

66.  The  sporogonimn. 
— In  its  fullest  devel- 
opment the  sporogoui- 
um is  differentiated 
into  the  three  regions, 
foot,  seta,  and  capsule 
(Figs.  82,  107)  ;  but  in 
some  forms  the  seta 
may  be  lacking,  and 
in  others  the  foot  also, 
the  sporogouium  in  this 
last  case  being  only  the 
capsule  or  spore  case, 
which,  after  all,  is  the 
essential  part  of  any 
sporogouium. 

At  first  the  capsule 
is  solid,  and  its  cells 
are  all  alike.  Later  a 
group  of  cells  within 
begins  to  differ  in  ap- 
pearance from  those 
about  them,  being  set 
apart  for  the  produc- 
tion of  spores.  This 
initial  group  of  spore-producing  cells  is  called  the  arche- 
spormm,  a  word  meaning  "the  beginning  of  spores."    It 


Fig.  85.  Sporogouium  of  Fimaria :  A,  an  em- 
bryo sporogonium  if,/'),  developiug  within 
the  venter  (6,  6)  of  an  archegonium  ;  B,  C, 
tips  of  leafy  shoots  bearing  young  sporo- 
gonia,  pushing  up  calyptra  (c)  and  archego- 
nium neck  {h),  and  sending  the  foot  down 
Into  the  apex  of  the  gametophore.— After 

GOEBEL. 


BRYOPIIYTES  103 

does  not  follow  that  the  archesporial  cells  themselves  pro- 
duce spores,  but  that  the  spores  are  to  appear  sooner  or 
later  in  their  progeny.  Usually  the  archesporial  cells 
divide  and  form  a  larger  mass  of  spore-producing  cells. 
Such  cells  are  known  as  s2Jorogenous  ("spore-producing") 
cells,  or  the  group  is  spoken  of  as  sporogenous  tissue.  Spo- 
rogenous  cells  may  divide  more  or  less,  and  the  cells  of  the 
last  division  are  mother  cells,  those  which  directly  produce 
the  spores.  The  usual  sequence,  therefore,  is  archesporial 
cells  (archesporium),  sporogenous  cells,  and  mother  cells ; 
but  it  must  be  remembered  that  they  all  may  be  referred 
to  as  sporogenous  cells. 

Each  mother  cell  organizes  within  itself  four  spores, 
the  group  being  known  as  a  tetrad.  In  Bryophytes  and 
the  higher  groups  asexual  spores  are  always  produced  in 
tetrads.  After  the  spores  are  formed  the  walls  of  the 
mother  cells  disorganize,  and  the  spores  are  left  lying  loose 
in  a  cavity  which  was  formerly  occupied  by  the  sporoge- 
nous tissue.  All  mother  cells  do  not  always  organize  spores. 
In  some  cases  some  of  them  are  used  up  in  supplying  nour- 
ishment to  those  which  form  spores.  Such  mother  cells  are 
said  to  function  as  nutritive  cells.  In  other  cases,  certain 
mother  cells  become  much  modified  in  form,  being  organ- 
ized into  elongated,  spirally-banded  cells  called  ektters  (Figs. 
97,  101),  meaning  "drivers"  or  "hurlers."  These  elaters 
lie  among  the  loose  ripe  spores,  are  discharged  with  them, 
and  by  their  jerking  movements  assist  in  scattering  them. 

The  cells  of  the  sporogonium  which  do  not  enter  into 
the  formation  of  the  archesporium,  and  are  not  sporoge- 
nous, are  said  to  be  sterile,  and  are  often  spoken  of  as 
sterile  tissue.  Every  sporogonium,  therefore,  is  made  up 
of  sporogenous  tissue  and  sterile  tissue,  and  the  differences 
found  among  the  sporogonia  of  Bryophytes  depend  upon 
the  relative  display  of  these  two  tissues. 

The  sporogonium  is  a  very  important  structure  from 
the  standpoint  of  evolution,  lor  it  represents  the  conspicu- 


104 


PLANT   STRUCTURES 


ous  part  of  the  higher  plants.  The  "  fern  plant,"  and 
the  herbs,  shrubs,  and  trees  among  "flowering  plants" 
correspond  to  the  sporogonium  of  Bryophytes,  and  not  to 
the  leafy  branch  (gametophore)  or  "moss  plant."  Conse- 
quently the  evolution  of  the  sporogonium  through  the 
Bryophytes  is  traced  with  a  great  deal  of  interest.  It  may 
be  outlined  as  follows  : 

In  a  liverwort  called  Kiccia  the  simplest  sporogonium 
is  found.     It  is  a  globular  capsule,  without   seta  or  foot 


Fig.  86.  Diagrammatic  sections  of  sporogoiiia  of  liverworts:  A.  Riccia,  the  whole 
capsule  being  archesporium  except  the  sterile  wall  layer ;  B,  Marchantia,  one 
half  the  capsule  being  sterile,  the  archesporium  restricted  to  the  other  half ;  Z>, 
Anthoceros,  archesporium  still  more  restricted,  being  dome-shaped  and  capping  a 
central  sterile  tissue,  the  columella  (col). — After  Gobbel. 


(Fig.  86,  A).  The  only  sterile  tissue  is  the  single  layer  of 
cells  forming  the  wall,  all  the  cells  within  the  wall  be- 
longing to  the  archesporium.  The  ripe  sporogonium, 
therefore,  is  nothing  but  a  thin-walled  spore  case.  It  is 
well  to  note  that  the  sporophyte  thus  begins  as  a  spore 
case,  and  that  any  additional  structures  that  it  may  de- 
velop later  are  secondary. 

In  another  liverwort  (M(irclianfia)  the  entire  lower  half 
of  the  sporogonium  is  sterile,  while  in  the  upper  half  there 


BRYOi'IIYTES 


105 


is  a  single  layer  of  sterile  cells  as  a  wall  about  the  arche- 
sporium,  which  is  composed  of  all  the  remaining  cells  of  the 
upper  half  (Fig.  8G,  B).  It  will  be  noted  that  the  sterile 
tissue  in  this  sporogonium  has  encroached  upon  the  arche- 
sporium,  which  is  restricted  to  one  half  of  the  body.  In 
this  case  the  archesporium  has  the  form  of  a  hemisphere. 

In  another  liverwort  {Jungermamria)  the  archesporium 
is  still  more  restricted  (Fig.  87).    The  sterile  tissue  is  organ- 


FiG.  87.  Diagrammatic  section  of  i?po- 
rogoninm  of  a  Jungermannia  form, 
showing  differentiation  into  foot, 
seta,  and  capsule,  the  archesporium 
restricted  to  upper  part  of  sporogo- 
nium.—After  GOEBEL. 


Fig.  88.  Section  through  sporogonium  of 
Sphagnum,  showing  capsule  (k)  with 
old  archegonium  neck  (ah),  calyptra  (ca), 
dome-shaped  mass  of  sporogenous  tissue 
(spo).  and  columella  {co).  also  the  bulb- 
ous foot  is])/)  imbedded  in  the  pseudo- 
podium  (;)*■).— After  ScuiMrEit. 


ized  into  a  foot  and  a  seta,  and  the  archesporium  is  a  com- 
paratively small  mass  of  cells  in  the  upper  part  of  the 
sporogonium. 

In  another  liverwort  {Aui//(iceros)  the  sterile  tissue  or- 
ganizes foot  and  seta,  and  the  archesporium  is  still  more 
restricted  (Fig.  8G,  D).     Instead  of  a  solid  hemispherical 


106 


PLANT    STEUCTUKES 


% 


mass,  it  is  a  dome-shaped  mass,  the  inner  cells  of  the  hemi- 
sphere having  become  sterile.  This  central  group  of  sterile 
cells  which  is  surrounded  by  the  ar- 
chesporium  is  called  the  columella, 
which  means  "^a  small  column." 

In  a  moss  called  Sphagnum  there 
is  the  same  dome-shaped  archespori- 
um  with  the  columella,  as  in  Ati- 
thoceros,  but  it  is  relatively  smaller 
on  account  of  the  more  abundant 
sterile  tissue  (Fig.  88). 

In  the  highest  Mosses  the  arche- 
sporium  becomes  very  small  as  com- 
pared with  the  sterile  tissue  (Fig. 
89).  A  foot,  a  long  seta,  and  an 
elaborate  capsule  are  organized  from 
the  sterile  tissue,  while  the  arche- 
sporium  is  shai^ed  like  the  walls  of 
a  barrel,  as  though  the  dome-shaped 
archesporium  of  Sphagnum  or  An- 
thoceros  had  become  sterile  at  the 
apex.  In  this  way  the  columella  is 
continued  through  the  capsule,  and 
is  not  capped  by  the  archesporium. 

This  series  indicates  that  after 
the  sporogonium  begins  as  a  simple 
spore  case  {Riccia),  its  tendency  is 
to  increase  sterile  tissue  and  to  re- 
strict sporogenous  tissue,  using  the 
sterile  tissue  in  the  formation  of  the 
organs  of  the  sporogonium  body,  as 
foot,  seta,  capsule  walls,  etc. 

Among  the  Green  Algfe  there  is 
a  form  known  as  Coleochcete,  whose 
body  resembles  those  of  the  sim- 
plest  Liverworts   (Fig.  90).      When 


Fig.  89.  Young  sporofroni- 
um  of  a  true  moss,  show- 
ing foot,  seta,  and  young 
capsule,  in  which  the  ar- 
chesporium (darker  por- 
tion') is  barrel-shaped,  and 
through  it  the  columella  is 
continuous  with  the  lid. — 
After  Campbell. 


BRYOPIIYTES 


107 


its  oospores  germiiifite  there  is  formed  a  globular  mass  of 
cells,  every  one  of  which  is  a  spore  mother  cell  (Fig.  90,  C). 
If  an  outer  layer  of  mother  cells  should  become  sterile  and 
form  a  wall  about  the  others,  such  a  spore  case  as  that  of 


Fig.  QO.—Coleoch(Efe,  one  of  the  green  algae:  A,  a  portion  of  the  thallus,  showing 
oogonia  with  trichogynes  (og),  antheridia  {««),  and  two  enlarged  biciliate  sperms 
(3);  B,  a  fertilized  oogonium  containing  oospore  and  invested  by  a  tissue  (r) 
which  has  developed  after  fertilization  ;  C,  an  oospore  which  has  germinated 
and  formed  a  mass  of  cells  (probably  a  sporophyte),  each  one  of  which  organizes 
a  biciliate  zoospore  (Z)).— After  Pringsheim. 


Riccia  would  be  the  result  (Fig.  86,  A).  For  such  reasons 
many  believe  that  the  Liverworts  have  been  derived  from 
such  forms  as  CoIeocJia'te. 

67.  The  gametophyte. — Having  considered  the  sporo- 
phyte body  as  represented  by  the  sporogonium,  we  must 
consider  the  gametophyte  body  as  represented  by  proto- 
nema  and  leafy  branch  (gametophore).  The  gametophyte 
results  from  the  germination  of  an  asexual  spore,  and  in 
the  Mosses  it  is  differentiated  into  protonema  and  leafy 
gametophore  (Figs.  81,  83,  102).      Like   the  sporophyte, 


IQg  PLANT    STKUCTUKES 

however,  it  shows  an  interesting  evolution  from  its  sim- 
plest condition  in  the  Liverworts  to  its  most  complex  con- 
dition in  the  true  Mosses. 

In  the  Liverworts  the  sj)ore  develops  a  flat  thallus  body, 
one  plate  of  cells  or  more  in  thickness,  which  generally 
branches  dichotomously  (see  §  29)  and  forms  a  more  or  less 
extensive  body  (Fig.  92).  This  thallus  is  the  gametophyte, 
there  being  no  differentiation  into  protonema  and  leafy 
branch. 

In  the  simpler  Liverworts  the  sex  organs  (antheridia 
and  archegonia)  are  scattered  over  the  back  of  this  thallus 
(Fig.  92).  In  other  forms  they  become  collected  in  certain 
definite  regions  of  the  thallus.  In  other  forms  these  defi- 
nite sexual  regions  become  differentiated  from  the  rest  of 
the  thallus  as  disks.  In  other  forms  these  disks,  bearing 
the  sex  organs,  become  short-stalked,  and  in  others  long- 
stalked,  until  a  regular  branch  arises  from  the  thallus 
body  (Figs.  96,  97).  This  erect  branch,  bearing  the  sex  or- 
gans, is,  of  course,  a  gametophore,  but  it  is  leafless,  the 
thallus  body  doing  the  chlorophyll  work. 

In  the  Sphagnum  Mosses  the  spore  develops  the  same 
kind  of  flat  thallus  (Fig.  104),  but  the  gametophore  be- 
comes leafy,  sharing  the  chlorophyll  work  with  the  thallus. 
In  the  true  Mosses  most  of  the  chlorophyll  work  is  done  by 
the  leafy  gametophore,  and  the  flat  thallus  is  reduced  to 
branching  filaments  (the  protonema)  (Fig.  102). 

The  protonema  of  the  true  Mosses,  therefore,  corre- 
sponds to  the  flat  thallus  of  the  Liverworts  and  SpJiagtinm, 
while  the  leafy  branch  corresponds  to  the  leafless  gameto- 
phore found  in  some  Liverworts.  It  also  seems  evident 
that  the  gametophore  was  originally  set  apart  to  bear  sex 
organs,  and  that  the  leaves  whicli  appear  upon  it  in  the 
Mosses  are  subsequent  structures. 


CHAPTEE   VIII 

THE  GREAT  GROUPS  OF  BRYOPHYTES 

Hepatic^  (Liverworts) 

68.  General  character. — Liverworts  live  in  a  variety  of 
conditions,  some  floating  on  the  water,  many  in  damp 
places,  and  many  on  the  bark  of  trees.  In  general  they  are 
moistnre-loving  plants  (hydrophytes),  though  some  can  en- 
dure great  dryness.  The  gametophyte  body  is  prostrate, 
though  there  may  be  erect  and  leafless  gametophores. 

This  prostrate  habit  develops  a  dorsiventral  body — that 
is,  one  whose  two  surfaces  {dorsal  and  vetitral)  are  exposed 
to  different  conditions  and  become  unlike  in  structure.  In 
Liverworts  the  ventral  surface  is  against  the  substratum, 
and  puts  out  hair-like  processes  {rhizoids)  for  anchorage 
and  possibly  absorption.  The  dorsal  region  is  exposed  to 
the  light  and  its  cells  develop  chlorophyll.  If  the  thalhis 
is  thin,  chlorophyll  is  developed  in  all  the  cells ;  if  it  be  so 
thick  that  the  light  is  cut  off  from  the  ventral  cells,  the 
thallus  is  differentiated  into  a  green  dorsal  region  doing  the 
chlorophyll  work,  and  a  colorless  ventral  region  producing 
anchoring  rhizoids.  This  latter  represents  a  simple  differ- 
entiation of  the  nutritive  body  into  working  regions,  the 
ventral  region  absorbing  material  and  conducting  it  to  the 
green  dorsal  cells  which  use  it  in  making  food. 

There  seem  to  have  been  at  least  three  main  lines  of 
development  among  Liverworts,  each  beginning  in  forms 
with  a  very  simple  thallus,  and  developing  in  different  di- 
rections.    They  are  briefly  indicated  as  follows : 

109 


110 


PLANT   STRUCTURES 


G9.  Marchantia  forms. — lu  this  line  the  simple  thallus 
gradually  becomes  changed  into  a  very  complex  one.     The 

thallus  retains  its  simple 
outlines,  but  becomes  thick 
and  differentiated  in  tissues 
(groups  of  similar  cells). 
The  line  may  be  distin- 
guished, therefore,  as  one 
in  which  the  differentia- 
tion of  the  tissues  of  the 
gametophyte  is  emphasized 
(Figs.  91-93).  In  Mar- 
cliantia  proper  the  thallus 
becomes  very  complex,  and 
it  may  be  taken  as  an  illus- 
tration. 

The  thallus  is  so  thick 

that  there  are  very  distinct 

green   dorsal   and  colorless 

ventral  regions  (Fig.  94).     The  latter  puts  out  numerous 

rhizoids  and  scales  from  the  single  layer  of  epidermal  cells. 

Above  the  ventral  epidermis  are  several  layers  of  colorless 


Fig.  91.  A  very  small  species  of  Riccia, 
one  of  the  Marchantia  forms  :  A,  a 
group  of  thallus  bodies  slightly  en- 
larged ;  B,  section  of  a  thallus,  show- 
ing rhizoids  and  two  sporogonia  im- 
bedded and  communicating  with  the 
outside  by  tubular  passages  in  the 
thallus. — After  Strasburger. 


Fig.  92.  Ricciocarpus,  a  Marchantia  form,  8ho\Ving  numerons  rhizoids  from  ventral 
surface,  the  dichotomous  branching,  and  the  position  of  the  sporogonia  on  the 
dorsal  surface  along  the  "midribs."— Goldbekger. 


Fig.  93.  Two  common  liverworts  :  to  the  left  is  Conocephalus,  a  Marchantia  form, 
showing  rhizoids,  dichotomous  branching,  and  the  conspicuous  rhombic  areas 
(areolae)  on  the  dorsal  surface;  to  the  right  is  Anthoceros,  with  its  simple  thallus 
and  pod-like  sporogonia.— Goldberger. 


Ficj.  94.  Cross-sections  of  thallus  of  Marchantia:  A,  section  from  thicker  part  of 
thallus,  where  supporting  ti-ssiic  {p]  is  abundant,  and  showing  lower  epidermis 
giving  rise  to  rhizoids  (/;)  and  plates  (J),  also  chlorojihyll  tissue  (chl)  organized 
into  chambers  by  partitions  (oi;  B,  section  near  margin  of  thallus  more  magnified, 
eliowing  lower  epidermis,  two  layers  of  supi)orting  tissue  ip)  with  reticulate  walls, 
a  single  chloroi)hyll  chamber  with  its  bounding  walls  is)  and  containing  short, 
often  branching  filaments  whose  cells  contain  chloroplasts  {chl),  overarching 
upper  epidermis  (o)  pierced  by  a  large  chimney-like  air-pore  («/>).— After  Goebel. 


Fig.  95.  Section  through  cupule  of  ilarchantia,  showing  wall  in  which  are  chloro- 
phyll-bearing air-chambers  with  air-pores,  and  gemmie  (a)  in  various  stages  of 
development. — Dodei.-Port. 


Fig.  96.  Marchantia  polymorpha :  the  lower  figure  represents  a  gametophyte  bear- 
ing a  mature  antheridial  branch  (d),  some  ybung  antheridial  branches,  and  also 
Bome  cupules  with  toothed  margins,  in  which  the  gemmae  may  be  seen ;  the 
upper  figure  represents  a  partial  section  through  the  antheridial  disk,  and  shows 
antheridia  within  the  antheridial  cavities  (a,  b,  c,  d,  €,/).— After  Knt. 


THE  GREAT   GROUPS   OF  BRYOPIIYTES 


113 


cells  more  or  less  modified  for  conduction.  Above  these 
the  dorsal  region  is  organized  into  a  series  of  large  air  cham- 
bers, into  which  project  chlorophyll-containing  cells  in  the 


Fig.  97.  Marchantia  polymorjiha,  a  common  liverwort :  i,  thallus.  witli  rhizoids, 
bearing  a  mature  archegonial  branch  (/)  and  several  younger  ones  (a,  h,  c,  d,  e); 
S  and  3,  dorsal  and  ventral  views  of  archegonial  disk;  U  and  5.  young  sporophyte 
(sporogonium)  embryos;  G.  more  mature  sporogonium  still  within  enlarged  venter 
of  archcgonium;  7,  mature  sporogonium  discharging  spores;  S,  three  spores  and 
an  ulatcr. — After  Kny. 


form  of  short  branching  filaments.  Overarching  the  air 
chambers  is  the  dorsal  epidermis,  and  piercing  through  it 
into  each  air  chamber  is  a  conspicuous  air  pore  (Fig.  94,  B). 


114 


PLANT   STRUCTUKES 


The  air  chambers  are  outlined  on  the   surface  as   small 

rhombic  areas  (areolw),  each  containing  a  single  air  pore. 

Peculiar  reproductive  bodies  are  also   developed  upon 

the  dorsal  surface  of  Marcltantia  for  vegetative  multiplica- 


FiG.  98.  Marchantia  poiytnori-)ha:  i,  partial  section  thronph  archegonial  disk,  ehow- 
ing  arcliegonia  with  long  necks,  and  venters  containing  eggs;  ,9,  young  archego- 
niiim  showing  axial  row;  10,  superficial  view  at  later  stage;  11,  mature  archego- 
nium,  with  axial  row  disorganized  and  leaving  an  open  passage  to  the  large  egg; 
n,  cross-section  of  venter;  13,  cross-section  of  neck.— After  Knt. 


tion.  Little  cups  (cnpules)  appear,  and  in  them  are  numer- 
ous short-stalked  bodies  {gemnm),  which  are  round  and 
flat  (biscuit-shaped)  and  many-celled  (Figs.  95,  96).     The 


THE   GREAT  GROUPS   OF  BRYOPIIYTES  H^ 

gemmae  fall  oif  and  develop  new  thallus  bodies,  making 
rapid  multiplication  possible. 

Marchantia  also  possess  remarkably  prominent  gameto- 
pliores,  or  "sexual  branches"  as  they  are  often  called. 
In  this  case  the  gametophores  are  differentiated,  one  bear- 
ing only  antheridia  (Fig.  96),  and  known  as  the  "anthe- 
ridial  branch,"  the  other  bearing  only  archegonia  (Figs.  97, 
98),  and  known  as  the  ''archegonial  branch."  The  scal- 
loped antheridial  disk  and  the  star-shaped  archegonial  disk, 
each  borne  up  by  the  stalk-like  gametophore,  are  seen  in  the 
illustrations.  Not  only  are  the  gametophores  sexually  dif- 
ferentiated, but  as  only  one  appears  on  each  thallus,  the  thal- 
lus bodies  are  sexually  differentiated.  When  the  two  sex 
organs  appear  upon  different  individuals,  the  j)lant  is  said  to 
be  dimcious,  meaning  "  two  households  "  ;  when  they  both 
appear  upon  the  same  individual,  the  plant  is  monoecious, 
meaning  "  one  household."  Some  of  the  Bryophytes  are  mo- 
noecious, and  some  of  them  are  dioecious  (as  3Iarchantia). 

Another  distinguishing  mark  of  the  line  of  Marchantia 
forms  is  that  the  capsule-like  sporogonium  opens  irregu- 
larly to  discharge  its  spores  (Fig.  97,  7). 

70.  Jungermannia  forms. — This  is  the  greatest  line  of 
the  Liverworts,  the  forms  being  much  more  numerous 
than  in  the  other  lines.  They  grow  in  damp  places  ;  or  in 
drier  situations  on  rocks,  ground,  or  tree-trunks  ;  or  in  the 
tropics  also  on  the  leaves  of  forest  plants.  They  are  gen- 
erally delicate  plants,  and  resemble  small  Mosses,  many  of 
them  doubtless  being  commonly  mistaken  for  Mosses. 

This  resemblance  to  Mosses  suggests  one  of  the  chief 
features  of  the  line.  Beginning  with  a  simple  thallus,  as 
in  the  Marcliantia  line,  the  structure  of  the  thallus  re- 
mains simple,  there  being  no  such  differentiation  of  tissues 
as  in  the  May'chayitia  line  ;  but  the  form  of  the  thallus 
becomes  much  modified  (Figs.  99,  100).  Instead  of  a  flat 
thallus  with  even  outline,  the  body  is  organized  into  a  cen- 
tral stem-like  axis  bearing  two  rows  of  small,  often  crowded 


116 


PLANT  STRUCTURES 


leaves.  There  are  really  three  rows  of  leaves,  but  the  third 
is  on  the  ventral  side  against  the  substratum,  and  is  often 
so  much  modified  as  not  to  look  like  the  other  leaves.  In 
consequence  of  this  the  Jungermannia  forms  are  usually 
called  "leafy  liverworts,"  to  distinguish  them  from  the 


Fig.  99.  Two  liverworts,  both  Jungermannia  forms:  to  the  left  is  Blasia,  which  re- 
tains the  thallus  form  but  has  lobed  margins;  to  the  right  is  Scapa?na,  with  dis- 
tinct leaves  and  sporogonia  (-4).— Goldberger. 


other  Liverworts,  which  are  '^thallose."  They  are  also 
often  called  "scale  mosses,"  on  account  of  their  moss-like 
appearance  and  their  small  scale-like  leaves. 

The  line  may  be  distinguished,  therefore,  as  one  in 
which  the  differentiation  of  the  form  of  the  gametophyte 
is  emphasized.  Another  distinguishing  mark  is  that  the 
sporogonium  has  a  prominent  seta,  and  the  capsule  splits 
down  into  four  pieces  (valves)  when  opening  to  discharge 
the  spores  (Fig.  100,  C). 

71.  Anthoceros  forms. — This  line  contains  comparatively 
few  forms,  but  they  are  of  great  interest,  as  they  are  sup- 
posed to  represent  forms  which  have  given  rise   to  the 


THE  GKEAT  GKOUPS  OF  BKYOFHYTES        H'j 


Fig.  100.  Species  of  Lepidosia,  a  genus  of  leafy  liverworts,  showing  different  leaf 
forms,  and  in  A  and  C  the  dehiscence  of  the  sporogoniiim  by  four  valves  In  C 
rhizoids  are  evident;  and  in  B,  D,  and  E  the  three  rows  of  leaves  are  seen,  the 
leaves  of  the  ventral  row  being  comparatively  small.-After  Engler  and  Prastl. 

-Mosses,   and  possibly  to    the   Pteridophytes   also.      The 
thallus   is   very   simple,   being    differentiated    neither   in 
structure  nor  form,  as  in  the  two  other  lines ;    but  the 
26 


118 


TLANT   STRUCTURES 


special   development    has    been   in   connection   with    the 
sporogonium  (Figs.  93,  101). 

This  complex  sporogonium  (sporophyte)  has  a  large 
bulbous  foot  imbedded  in  the  simple  thallus,  while 
above  there  arises  a  long  pod-like  capsule.  The  com- 
plex walls  of  this  cap- 
sule contain  chlorophyll 
and  air  pores,  so  that 
the  sporogonium  is  or- 
ganized for  chlorophyll 
work.  If  it  could  send 
absorbing  roots  into  the 
soil,  this  sporophyte 
could  live  independent 
of  the  gametophyte.  In 
opening  to  discharge 
spores  the  pod-like  cap- 
sule splits  down  into 
two  valves. 

Another    peculiarity 

of  the  Anthoceros  forms 

is   in     connection    with 

i       ji  W    '  )      '         M  ^       M        ^^^®  antheridia  and  arch- 

\v  11  m-^.~)  ^^^,^   ^^&^       M        egonia.      These   organs, 

instead  of  growing  out 
free  from  the  body  of  the 
thallus,  as  in  other  Liv- 
erworts, are  imbedded  in 
it.     The  significance  of 
this    peculiarity  lies    in 
the  fact  that  it  is  a  char- 
acter which   belongs   to 
the  Pteridophytes. 
The  chief  direction  of  development  of  the  three  liv- 
erwort lines  may  be  summed  up  briefly  as  follows  :   The 
MarcJiantia  line  has  differentiated   the   structure  of  the 


Fig.  101.  Anthoceros  gracilis :  A,  several 
gametophytes,  on  which  sporogonia  have 
developed  ;  J5,  an  enlarged  sporogonium, 
showing  its  elongated  character  and  de- 
hiscence by  two  valves  leaving  exposed 
the  slender  columella  on  the  surface  o^ 
which  are  the  spores;  C,  D,  E,  F,  ela- 
ters  of  various  forms  ;  G,  spores. — After 
ScniFFNER. 


THE  GEEAT  GROUPS  OF  'BEYOPHYTES       HQ 

gametophyte  ;  the  Jungermannia  line  has  differentiated 
the  form  of  the  gametophyte  ;  the  Anthoceros  line  has 
differentiated  the  structure  of  the  sporophyte.  It  should 
be  remembered  that  other  characters  also  serve  to  distin- 
guish the  lines  from  one  another. 

Musci  (Mosses) 

72.  General  character. — Mosses  are  highly  specialized 
plants,  probably  derived  from  Liverworts,  the  numerous 
forms  being  adapted  to  all  conditions,  from  submerged  to 
very  dry,  being  most  abundantly  displayed  in  temperate 
and  arctic  regions.  Many  of  them  may  be  dried  out  com- 
pletely and  then  revived  in  the  presence  of  moisture,  as  is 
true  of  many  Lichens  and  Liverworts,  with  which  forms 
Mosses  are  very  commonly  associated. 

They  also  have  great  power  of  vegetative  multiplica- 
tion, new  leafy  shoots  putting  out  from  old  ones  and  from 
the  protonema  indefinitely,  thus  forming  thick  carpets  and 
masses.  Bog  mosses  often  completely  fill  up  bogs  or  small 
ponds  and  lakes  with  a  dense  growth,  which  dies  below 
and  continues  to  grow  above  as  long  as  the  conditions  are 
favorable.  These  quaking  bogs  or  "mosses,"  as  they  are 
sometimes  called,  furnish  very  treacherous  footing  unless 
rendered  firmer  by  other  plants.  In  these  moss-filled  bog? 
the  water  shuts  off  the  lower  strata  of  moss  from  complete 
disorganization,  and  they  become  modified  into  a  coaly  sub- 
stance called  peat,  which  may  accumulate  to  considerable 
thickness  by  the  continued  upward  growth  of  the  mass  of 
moss. 

Tlie  gametophyte  body  is  differentiated  into  two  very 
distinct  regions :  (1)  the  prostrate  dorsiventral  thallus, 
which  is  called  protonema  in  this  group,  and  which  may  be 
either  a  broad  flat  thallus  (Fig.  104)  or  a  set  of  branching 
filaments  (Figs.  81,  102) ;  (2)  the  erect  leafy  branch  or 
gametophore  (Fig.  82).     This  erect  branch  is  said  to  be 


120 


PLANT   STKUCTUKES 


radial,  in  contrast  with  the  dorsiventral  thallus,  referring 
to  the  fact  that  it  is  exposed  to  similar  conditions  all 
around,  and  its  organs  are  arranged  about  a  central  axis 
like  the  parts  of  a  radiate  animal.     This  position  is  much 

more  favorable  for  the 
chlorophyll  work  than 
the  dorsiventral  posi- 
tion, as  the  special 
chlorophyll  organs 
(leaves)  can  be  spread 
out  to  the  light  freely 
in  all  directions. 

It  should  be  re- 
marked that  the  gam- 
etophyte  in  all  groups 
of  plants  is  a  thallus, 
doing  its  chlorophyll 
work,  when  it  does 
any,  in  a  dorsiventral 
position  ;  the  only  ex- 
ception being  the  ra- 
dial leafy  branch  that 
arises  from  the  thal- 
lus of  Mosses.  From 
Mosses  onward  the 
gametophyte  becomes 
less  conspicuous,  so 
that  the  prominent 
leafy  plants  of  the 
higher  groups  hold  no 
relation  to  the  little  erect  leafy  branch  of  the  Mosses, 
which  is  put  out  by  the  gametophyte,  and  which  is  the 
best  the  gametophyte  ever  does  toward  getting  into  a  bet- 
ter position  for  chlorophyll  work- 

The  leafy  branch  of  the  Mosses  usually  becomes  inde- 
pendent of  the  thallus  by  putting  out  rhizoids  at  its  base 


Fig.  102.  A  moss  (Bryi/tn),  showing  base  of  a 
leafy  branch  (gametophore)  attached  to  tlie 
protonema.  and  having  sent  out  rhizoids.  On 
the  protonemal  filament  to  the  right  and  be- 
low is  the  young  bud  of  another  leafy  branch. 

— MULLEK. 


THE  GKEAT  GROUPS  OF  BKYOPIIYTES 


121 


(Fig.  102),  the  thallus  part  dying.  Sometimes,  however, 
the  filamentous  protonema  is  very  persistent,  and  gives  rise 
to  a  perennial  succession  of  leafy  branches. 

A  :P 


Fig.  103.  Tip  of  leafy  branch  of  a  moss  (Ftmaria),  bearing  a  cluster  of  sex  organs, 
showing  an  old  antheridium  (A),  a  younger  one  (B),  some  of  the  curious  associated 
hairs  (p),  and  leaf  sections  (/).— After  Campbell. 


At  the  summit  of  the  leafy  gametophore,  either  upon 
the  main  axis  or  upon  a  lateral  branch,  the  antheridia  and 
archegonia  are  borne  (Figs.  83,  103).  Often  the  leaves  at 
the  summit  become  modified  in  form  and  arranged  to  form 


122 


PLANT   STRUCTUKES 


a  rosette,  in  the  center  of  which  are  the  sex  organs.  This 
rosette  is  often  called  the  "moss  flower,"  but  it  holds  no 
relation  to  the  flower  of  Seed-plants,  and  the  phrase  should 
not  be  used.  A  rosette  may  contain  but  one  kind  of  sex 
organ  (Figs,  83,  103),  or  it  may  contain  both  kinds,  for 
Mosses  are  both  dioecious  and  moncecious.  The  two  prin- 
cipal groups  are  as  follows  : 

73.  Sphagnum  forms. — These  are  large  and  pallid  bog 
mosses,  found  abundantly  in  marshy  ground,  especially  of 
temperate  and  arctic  regions,  and  are  conspicuous  peat- 
formers  (Fig.  105,  A).     The  leaves  and  gametophore  axis 

are  of  peculiar  struc- 
ture to  enable  them 
to  suck  up  and  hold 
a  large  amount  of  wa- 
ter. This  abundant 
water  -  storage  tissue 
and  the  comparative- 
ly poor  display  of 
chlorophyll  -  contain- 
ing cells  gives  the 
peculiar  pallid  ap- 
pearance. 

They  resemble  the 
Liverworts  in  the 
broad  thallus  body 
of  the  gametophyte, 
from  which  the  lai-ga 
leafy  gametophore 
arises  (Fig.  104). 
They  also  resemble 
Anthoceros  forms  in  the  sporogonium,  the  archesporium 
being  a  dome-shaped  mass  (Fig.  105,  C).  On  the  other 
hand,  they  resemble  the  true  Mqsses,  not  only  in  the  leafy 
gametophore,  but  also  in  the  fact  that  the  capsule  opens 
at  the  apex  by  a  circular  lid,  called  the  operculum  (Fig. 


Fig.  104.  Thallus  body  of  gametophyte  of  Sphag- 
nvm,  giving  rise  to  rhizoids  (r)  and  buds  (A) 
which  develop  into  the  large  leafy  branches 
(gametophores).— After  Campbell. 


THE  GREAT  GROUPS  OF  BRYOPIIYTES 


123 


105,  D),  which  means  a  "cover"  or  "lid."  This  may 
serve  to  illustrate  what  is  called  an  "intermediate"  or 
"transition"  type,  Sphagnum  showing  characters  which 
ally  it  to  Anthoceros  forms  on  the  one  side,  and  to  true 
Mosses  on  the  other. 

A  peculiar  feature  of  the  sporogonium  is  that  it  has  no 
long  stalk-like"  seta,  as  have  the  true  Mosses,  although  it 
appears  to  have  one.    This  false  appearance  arises  from  the 


Fig.  105.  Sphagnum :  A,Q.  leafy  branch  (gametophore)  bearing  four  mature  sporo- 
gonia;  B,  archegoniuin  in  whose  venter  a  young  embryo  sporophyte  (em)  is  de- 
veloping:' C,  section  of  a  young  sporogonium  (sporophyte),  showing  the  bulbous 
foot  (spf)  imbedded  in  the  apex  of  the  pseudopodium  (ps),  the  capsule  (A),  the 
columella  icd)  cai)pcd  by  the  dome-shaped  archesporium  (spo),  a  portion  of  the 
calyptra  (ca).  and  the  old  archegonium  neck  {ah)\  D,  branch  bearing  mature 
sporogonium  and  showing  pseudopodium  (ps),  capsule  (k),  and  operculum  (d)\  E, 
antheridium  discharging  sperms;  F,  a  single  sperm,  showing  coiled  body  and  two 
cilia.— After  Scuimper. 


fact  that  the  axis  of  the  gametophore  is  prolonged  above 
its  leafy  portion,  the  prolongation  resembling  the  seta  of 
an   ordinary  moss   (Fig.   105,  D).      This   prolongation   is 


124 


PLANT   STKUCTUKES 


called  a  pseudopodium,  or  "false  stalk,"  and  in  the  top  of 
it  is  imbedded  the  foot  of  the  sporogoninm  carrying  the 
globular  capsule  (Fig.  105,  C). 

74.  True  Mosses. — This  immense  and  most  highly  organ- 
ized Bryophyte  group  contains  the  great  majority  of  the 
Mosses,  which  are  sometimes  called  the  Bnjnm  forms,  to 
distinguish  them  from  the  Spliaynum  forms.      They  are 


Fig.  106.  Different  stages  in  the  development  of  the  leafy  gametophore  from  the  pro- 
tonema  of  a  common  moss  {Funarlay.  A,  the  first  few  cells  and  a  rhizoid  (r);  B, 
C,  later  stages,  showing  apical  cell  (1)  and  young  leaves  (i');  i),  later  stage  much 
less  magnified,  showing  protonemal  filaments  and  the  young  gametophore  {gam) 
— After  Campbell. 


the  representative  Bryophytes,  the  only  group  vying  with 
them  being  the  leafy  Ijiverworts,  or  Jungermannia  forms. 
They  grow  in  all  conditions  of  moisture,  from  actual  sub- 
mergence in  water  to  dry  rocks,  and  they  also  form  exten- 
sive peat  deposits  in  bogs. 

The  thallus  body  of  the  gametophyte  is  made  up  of 
branching  filaments  (Figs.  81,  102),  those  exposed  to  the 


THE  GREAT  GROUPS  OF  BRYOPHYTES 


125 


light  containing  chlorophyll,  and  those  in  the  substratum 
being  colorless  and  acting  as  rhizoids.  The  leafy  gameto- 
phores  are  often  highly  organized  (Figs.  102,  106),  the 
leaves  and  stems  showing  a  certain  amount  of  differentia- 
tion of  tissues. 

It  is  the  sporophyte,  however,  which  shows  the  great- 
est amount  of  specialization  (Fig.  107).     The  sporogonium 


Fig.  107.  A  common  moss  (Funaria):  in  the  center  is  the  leafy  shoot  (gametophore), 
with  rhizoids,  several  leaves,  and  a  sporogonium  (sporophyte),  with  a  long  seta, 
capsule,  and  at  its  tip  the  calyptra  (col):  to  the  right  a  capsule  with  calyptra  re- 
moved, showinK  the  operculum  (o);  to  the  left  a  young  sporogonium  pushing  up 
the  calyptra  from  the  leafy  shoot.— After  Campbell. 


has  a  foot  and  a  long  slender  seta,  but  the  capsule  is  espe- 
cially complex.  The  archesporium  is  reduced  to  a  small 
hollow  cylinder  (Fig.  88),  the  capsule  wall  is  most  elabo- 
rately constructed,  and  the    columella  runs  through  the 


Fig.  108.  Longitiuliiuil  section  of  moss  capsule 
{Funcuia),  showing  its  complex  character: 
d,  operculum;  /),  peristome:  c,  c',  columel- 
la; s,  sporogenous  tissue;  outside  of  s  the 
complex  wall  consisting  of  layers  of  cells 
and  large  open  spaces  {h)  traversed  by 
strands  of  tissue.— After  Goebel. 


Fig.  110.  Sporogonia  of  Grimmia,  from  all  of 
which  the  operculum  has  fallen,  displaying 
the  peristome  teeth :  A,  position  of  the  teeth 
when  dry ;  B,  position  when  moist.— After 
Kerner.  > 


Fig.  109.  Partial  longitudinal 
section  through  a  moss  cap- 
sule :  A,  younger  capsule, 
showing  wall  cells  (a),  cells 
of  columella  (il,  and  sporog- 
enous cells  {m) ;  B,  some- 
what older  capsule,  a  and  i 
same  as  before,  and  sm  the 
spore  mother  cells. —After 
Goebel. 


THE  GKEAT  GROUPS  OF  BRYOrilYTES       127 

center  of  the  capsule  to  the  lid-like  operculum  (Figs.  108, 
109).  When  the  operculum  falls  oil  the  capsule  is  left  like 
an  urn  full  of  spores,  and  at  the  mouth  of  the  urn  there  is 
usually  displayed  a  set  of  slender,  often  very  beautiful  teeth 
(Fig.  110),  converging  from  the  circumference  toward  the 
center,  and  called  the  peristome^  meaning  "  about  the 
mouth."  These  teeth  are  hygroscopic,  and  by  bending 
inward  and  outward  help  to  discharge  the  spores. 


CHAPTEE  IX 

PTERIDOPHYTES  (FERN  PLANTS) 

75.  Summary  from  Bryophytes. — In  introducing  the  Bryo- 

pliytes  a  summary  from  the  Thallophytes  was  given  (see  § 
60),  indicating  certain  important  things  which  that  group 
has  contributed  to  the  evolution  of  the  plant  kingdom. 
In  introducing  the  Pteridophytes  it  is  well  to  notice  certain 
important  additions  made  by  the  Bryophytes. 

(1)  Alternation  of  generations. — The  great  fact  of  alter- 
nating sexual  (gametophyte)  and  sexless  (sporophyte)  gen- 
erations is  first  clearly  expressed  by  the  Bryophytes,  although 
its  beginnings  are  to  be  found  among  the  Thallophytes. 
Each  generation  produces  one  kind  of  spore,  from  which  is 
developed  the  other  generation. 

(2)  Gametophyte  the  chlorojih  i/ll generation. — On  account 
of  this  fact  the  food  is  chiefly  manufactured  by  the  gameto- 
phyte, which  is  therefore  the  more  conspicuous  generation. 
When  a  moss  or  a  liverwort  is  spoken  of,  therefore,  the 
gametophyte  is  usually  referred  to. 

(3)  Gametophyte  and  sporophyte  7iot  independent. — The 
sporophyte  is  mainly  dependent  upon  the  gametophyte  for 
its-  nutrition,  and  remains  attached  to  it,  being  commonly 
called  the  sporogonium,  and  its  only  function  is  to  produce 
spores. 

(4)  Differentiation  of  thallus  into  stem  and  leaves. — 
This  appears  incompletely  in  the  leafy  Liverworts  {Jwiger- 
mannia  forms)  and  much  more  clearly  in  the  erect  and 
radial  leafy  branch  (gametophore)  of  the  Mosses. 

138 


PTERIDOPIiYTES  129 

(5)  Many-celled  sex  organs. — The  anthericlia  and  the 
flask-shaped  archegonia  are  very  characteristic  of  Bryo- 
phytes  as  contrasted  with  Thallophytes. 

76.  General  characters  of  Pteridophytes. — The  name  means 
"fern  plants,"  and  the  Ferns  are  the  most  numerous  and  the 
most  representative  forms  of  the  group.  Associated  with 
them,  however,  are  the  Horsetails  (Scouring  rushes)  and 
the  Club-mosses.  By  many  the  Pteridophytes  are  thought 
to  have  been  derived  from  such  Liverworts  as  the  Antlio- 
ceros  forms,  while  some  think  that  they  maj  possibly  have 
been  derived  directly  from  the  Green  Algce.  Whatever 
their  origin,  they  are  very  distinct  from  Bryophytes. 

One  of  the  very  important  facts  is  the  appearance  of 
the  vascular  system,  which  means  a  "system  of  vessels," 
organized  for  conducting  material  through  the  plant  body. 
The  appearance  of  this  system  marks  some  such  epoch  in 
the  evolution  of  plants  as  is  marked  in  animals  by  the 
appearance  of  the  "backbone."  As  animals  are  often 
grouped  as  "vertebrates"  and  "invertebrates,"  plants  are 
often  groujjed  as  "vascular  plants"  and  "non-vascular 
j)lants,"  the  former  being  the  Pteridophytes  and  Spermato- 
phytes,  the  latter  being  the  Thallophytes  and  Bryophytes. 
Pteridophytes  are  of  great  interest,  therefore,  as  being  the 
first  vascular  plants, 

77.  Alternation  of  generations. — This  alternation  con- 
tinues in  the  Pteridophytes,  but  is  even  more  distinct  than 
in  the  Bryoj)hytes,  the  gametophyte  and  sporoj)hyte  be- 
coming independent  of  one  another.  An  outline  of  the  life 
history  of  an  ordinary  fern  will  illustrate  this  fact,  and  will 
serve  also  to  point  out  the  prominent  structures.  Upon  the 
lower  surface  of  the  leaves  of  an  ordinary  fern  dark  spots 
or  lines  are  often  seen.  These  are  found  to  yield  spores, 
with  Avhich  the  life  history  may  be  begun. 

When  such  a  spore  germinates  it  gives  rise  to  a  small, 
green,  heart-shaped  thallus,  resembling  a  delicate  and  sim- 
ple liverwort  (Fig.  Ill,  A).     Upon  this  thallus  antheridia 


130 


PLANT   STEUCTUKES 


and  archegonia  appear,  so  that  it  is  evidently  a  gameto- 
phyte.  This  gametophyte  escapes  ordinary  attention,  as  it 
is  usually  very  small,  and  lies  prostrate  upon  the  substra- 
tum. It  has  received  the  name  prothalUum  or  prothallus, 
so  that  when  the  term  prothallium  is  used  the  gametophyte 
of  Pteridophytes  is  generally  referred  to  ;  j  ust  as  when  the 
term  sporogonium  is  used  the  sporophyte  of  the  Bryophytes 
is  referred  to.  Within  an  archegonium  borne  upon  this  little 
prothallium  an  oospore  is  formed.     When  the  oospore  ger- 


FiG.  111.  Prothallium  of  a  common  fern  (Aspidimii):  A,  ventral  surface,  showing 
rhizoids  (?'/i),  antheridia  (an),  'inrt  archegonia  {ar) ;  B,  ventral  surface  of  an  older 
gametophyte,  showing  rhizoids  (?7i)  and  young  sporophyte  with  root  (w)  and  leaf 
(&).— After  ScuENCK. 

minates  it  develops  the  large  leafy  plant  ordinarily  spoken 
of  as  "the  fern,"  with  its  subterranean  stem,  from  which 
roots  descend,  and  from  which  large  branching  leaves  rise 
above  the  surface  of  the  ground  (Fig.  Ill,  i?).  It  is  in 
this  complex  body  that  the  vascular  system  appears.  No 
sex  organs  are  developed  upon  it,  but  the  leaves  bear  numer- 
ous sporangia  full  of  asexual  spores.  This  complex  vascular 
plant,  therefore,  is  a  sporophyte,  and  corresponds  in  this 
life  history  to  the  sporogonium  of  the  Bryophytes.     This 


PTEEIDOrilYTES  131 

completes  the  life  cycle,  as  the  asexual  spores  develop  the 
prothallium  again. 

In  contrasting  this  life  history  with  that  of  Bryophytes 
several  important  differences  are  discovered.  The  most 
striking  one  is  that  the  sporophyte  has  become  a  large, 
leafy,  vascular,  and  independent  structure,  not  at  all  re- 
sembling its  representative  (the  sporogonium)  among  the 
Bryophytes. 

Also  the  gametophyte  is  much  less  prominent  than  the 
gametophytes  of  the  larger  Liverworts  and  Mosses.  If 
Ferns  have  been  derived  from  the  Liverworts,  therefore,  it 
is  probable  that  they  came  from  those  with  very  simple 
bodies  rather  than  from  those  in  which  the  gametophyte 
had  become  large  and  complex.  The  conspicuous  leafy 
branch  of  the  Mosses,  commonly  called  "  the  moss  plant," 
corresponds  to  nothing  in  the  Pteridophytes,  the  prothal- 
lium representing  only  the  protonema  part  of  the  gameto- 
phyte of  the  true  Mosses. 

The  small  size  of  the  gametophyte  seems  to  be  associ- 
ated with  the  fact  that  the  chlorophyll  work  has  been 
transferred  to  the  sporophyte,  which  hereafter  remains  the 
conspicuous  generation.  The  "  fern  plant "  of  ordinary 
observation,  therefore,  is  the  sporophyte  ;  while  the  "  moss 
plant  '*'  is  a  leafy  branch  of  the  gametophyte. 

Another  important  contrast  indicated  is  that  in  Bryo- 
phytes the  sporophyte  is  dependent  upon  the  gametophyte 
for  its  nutrition,  remaining  attached  to  it ;  Avhile  in  most 
of  the  Pteridophytes  both  generations  are  independent 
green  plants,  the  leafy  sporophyte  remaining  attached  to 
the  small  gametophyte  only  while  beginning  its  growth 
(Fig.  Ill,  B). 

Among  the  Ferns  some  interesting  exceptions  to  this 
method  of  alternation  have  been  observed.  Lender  certain 
conditions  a  leafy  sporophyte  may  sprout  directly  from  the 
prothallium  (gametophyte)  instead  of  from  an  oospore. 
This  is  called  ajwgamy,  meaning  "  without  the  sexual  act." 


;[32  PLANT   STKUCTUKES 

Under  certain  other  conditions  prothallia  are  observed  to 
sprout  directly  from  the  leafy  sporophyte  instead  of  from 
a  spore.  This  is  called  apospoi-y,  meaning  "  without  a 
spore." 

78.  The  gametophyte. — The  prothallium,  like  a  simple 
liverwort,  is  a  dorsiventral  body,  and  puts  out  numerous 


Fig.  112.  Stag-horn  fern  (Plaiycerinm  grande),  an  epiphytic  tropical  form,  showing 
the  two  forms  of  leaves  :  a  and  b,  young  sterile  leaves  ;  c,  leaves  bearing  spo- 
rangia ;  d,  an  old  sterile  leaf. — Caldwell. 


rhizoids  from  its  ventral  surface  (Fig.  111).  It  is  so  thin 
that  all  the  cells  contain  chlorophyll,  and  it  is  usually  short- 
lived.    In  rare  cases  it  becomes  quite  large  and  permanent, 


Fig.  113.  Archegonium  of  Pteris  at  the  tune  of  fertilization,  showing  tissue  of  gam- 
etophyte  {A),  the  cells  forming  the  neck  {B),  the  passageway  formed  by  the  dis- 
organization of  the  canal  cells  (C),  and  the  egg  (D)  lying  exposed  in  the  venter. 
— Caldwell. 


Fig.  114.  Antheridium  of  PlerwiB).  showing  wall  cells  (a),  opening  for  escape  of 
sperm  mother  cells  ie),  escaped  mother  cells  (c),  sperms  free  from  mother  cells  (6), 
showing  spiral  and  multiciliate  character. — Caldwell. 


27 


134 


PLANT   STRUCTURES 


being  a  conspicuo^^s  object  in  connection  with  the  sporo- 
phyte. 

At  the  bottom  of  the  conspicuous  notch  in  the  prothal- 
lium  is  the  growing  point, 
representing  the  apex  of  the 
plant.     This  notch  is  always 
a  conspicuous  feature. 

The  antheridia  and  arch- 
egonia  are  usually  developed 
on  the  under  surface  of  the 
prothallium  (Fig.  Ill,  A), 
and  differ  from  those  of  all 
Bryophytes,  except  the  An- 
thoceros  forms,  in  being  sunk 
in  the  tissue  of  the  prothal- 
lium and  opening  on  the  sur- 


PiG.  115.  Development  of  gametophyte 
of  Pteris:  the  figure  to  the  left  shows 
the  old  spore  (B),  the  rhizoid  (C),  and 
the  thallus  (^4);  that  to  the  right  is 
older,  showing  the  same  parts,  and 
also  the  apical  cell  (Z>). — Caldwell. 


Fig.  116.  Young  gametophyte  of  Pteris, 
showing  old  spore  wall  (B),  rhizoids 
(C),  apical  cell  (2)),  a  young  anther- 
idium  (E),  and  an  older  one  in  which 
sperms  have  organized  (i?').— Cald- 
well. 


PTEKIDOPIIYTES 


135 


face,  more  or  less  of  the  neck  of  the  archegonium  projecting 
(Fig.  113).  The  eggs  are  not  different  from  those  formed 
witliiii  the  areliegonia  of  Bryophytes,  but  the  sperms  are 
very  different.  Tlie  Bryophyte  sperm  has  a  small  body  and 
two  long  cilia,  while  tlie  Pteridophyte  sperm  has  a  long 
spirally  coiled  body,  blunt  behind  and  tapering  to  a  point  in 
front,  where  numerous  cilia  are  developed  (Fig.  114).  It 
is,  therefore,  a  large,  spirally-coiled,  multiciliate  sperm,  and 
is  quite  characteristic  of  all  Pteridophytes  excepting  the 
Club-mosses.  It  is  evident  that  a  certain  amount  of  water 
is  necessary  for  fertilization — in  fact,  it  is  needed  not  only 


Fig.  117.  Sections  of  portions  of  the  gametophyte  of  Pteris,  showing  development 
of  archegonium:  .-1,  young  stage,  showing  cells  which  develop  the  neck  (a),  and 
the  cell  from  which  the  egg  cell  and  canal  cells  develop  (b):  B,  an  older  stage, 
showing  neck  cells  (a\  neck  canal  cell  (6).  and  cell  from  which  is  derived  the  egg 
cell,  and  the  ventral  canal  cell  (c);  C,  a  still  older  stage,  showing  increased  num- 
ber of  neck  cells  {a),  two  neck  canal  cells  (A),  the  ventral  canal  cell  (c),  and  the 
cell  in  which  the  egg  is  organized  (rf). — Caldwell. 


by  the  swimming  sperm,  but  also  to  cause  the  opening  of 
tlie  antheridium  and  of  the  archegonium  neck.  There 
seems  to  be  a  relation  between  the  necessity  of  water  for 
fertilization  and  a  prostrate,  easily  moistened  gametophyte. 
Prothallia  are  either  monoecious  or  dioecious  (see  §  69). 
"Wlien  the  prothallia  are  developing  (Fig.  115)  the  anther- 


Fig.  118.  A  fern  {Aspidhim),  showing  three  large  branching  leaves  coming  from  a 
horizontal  subterranean  stem  (rootstock);  young  leaves  are  al.^o  shown,  which 
show  circinate  vernation.  The  stem,  young  leaves,  and  petioles  of  the  large 
leaves  are  thickly  covered  with  protecting  hairs.  The  stem  gives  rise  to  numerous 
small  roots  from  its  lower  surface.  The  figure  marked  3  represents  the  under  sur- 
face of  a  portion  of  the  leaf,  showing  seven  sori  with  shield-like  indusia;  at ;:  is 
represented  a  section  through  a  sorus.  showing  the  sporangia  attached  and  pro- 
tected by  the  indusium;  while  at  6  is  represented  a  single  sporangium  opening 
and  discharging  its  spores,  the  heavy  annulus  extending  along  the  back  and  over 
the  top. — After  Wossidlo. 


PTERIDOPUYTES 


13Y 


idia  begin  to  appear  very  early  (Fig.  110),  and  later  the 
archegonia  (Fig.  117).  If  the  prothalliiim  is  poorly  nour- 
ished, only  antheridia  appear ;  it  needs  to  be  well  developed 
and  nourished  to  develop  archegonia.  There  seems  to  be 
a  very  definite  relation,  therefore,  between  nutrition  and 
the  development  of  the  two  sex  organs,  a  fact  which  must 
be  remembered  in  connection  with  the  development  of 
beterospory. 

79.  The  sporophyte. — This  complex  body  is  differentiated 
into  root,  stem,  and  leaf,  and  is  more  highly  organized 
than  any  plant  body  heretofore  mentioned  (Fig.  118).  The 
development  of  this  body  and  its  three  great  working  regions 
must  be  considered  separately. 

(1)  Development  of  embryo. — The  oospore,  from  which 
the  sporophyte  develops,  rests  in  the  venter  of  the  arche- 
gonium,  which  at  this  stage  resembles  a  depression  in  the 


Fig.  119.  Embryos  of  a  common  fern  (Pteris):  A,  young  embryo,  showing  direction 
of  basal  wall  (/).  and  of  second  walls  (11),  which  organize  quadrants,  each  of 
which  subsequently  develops  into  foot  (/),  root  (w).  leaf  (ft),  and  stem  is):  B,  an 
older  embryo,  in  which  the  four  regions  (lettered  as  in  ,4)  have  developed  further, 
also  showing  venter  of  archegonium  (aiv),  and  some  tissue  of  the  prothallium  (pr). 
—A  after  Kiemtz-CJeuloff;  B  after  Hofmeister. 

lower  surface  of  the  prothallium  (Fig.  119,  B).  It  germi- 
nates at  once,  as  in  Bryophytes,  not  being  a  resting  spore 
as  in  Green  Algse.    The  resting  stage,  as  in  the  Bryophytes, 


138  FLANT   STRUCTURES 

is  in  connection  with  the  asexual  spores,  which  may  be 
kept  for  a  long  time  and  then  germinated. 

The  first  step  in  germination  is  for  the  oospore  to  di- 
vide into  two  cells,  forming  a  two-celled  embryo.  In  the 
ordinary  Ferns  this  first  dividing  wall  is  at  right  angles  to 
the  surface  of  the  prothallium,  and  is  called  the  basal  wall 
(Fig.  119,  A).  One  of  the  two  cells,  therefore,  is  anterior 
(toward  the  notch  of  the  prothallium),  and  the  other  is 
posterior. 

The  two  cells  next  divide  by  forming  walls  at  right 
angles  to  the  basal  wall,  and  a  four-celled  embryo  is  the 
result.  This  is  called  the  "quadrant  stage"  of  the  em- 
bryo, as  each  one  of  the  four  cells  is  like  the  quadrant  of  a 
sphere. 

With  the  appearance  of  the  quadrant,  four  body  regions 
are  organized,  each  cell  by  its  subsequent  divisions  giving 
rise  to  a  distinct  working  region  (Fig.  119,  A).  Two  of  the 
cells  are  inner  (away  from  the  substratum)  ;  also  one  of  the 
inner  and  one  of  the  outer  (toward  the  substratum)  cells 
are  anterior  ;  while  the  two  other  inner  and  outer  cells  are 
posterior.  The  anterior  outer  cell  develops  the  first  leaf  of 
the  embryo,  generally  called  the  cotyledon  (Fig.  119,  b)  ;  the 
anterior  inner  cell  develops  the  stem  (Fig.  119,  s) ;  the  pos- 
terior outer  cell  develops  the  first  (primary)  root  (Fig. 
119,  w)  ;  the  posterior  inner  cell  develops  a  special  organ 
for  the  use  of  the  embryo,  called  the  foot  (Fig.  119,  /). 
The  foot  remains  in  close  contact  with  the  prothallium  and 
absorbs  nourishment  from  it  for  the  young  embryo.  When 
the  young  sporophyte  has  developed  enough  to  become  in- 
dependent the  foot  disappears.  It  is  therefore  spoken  of 
as  a  temporary  organ  of  the  embryo.  It  is  necessary  for  the 
leaf  to  emerge  from  beneath  the  prothallium,  and  it  may 
be  seen  usually  curving  upward  through  the  notcli.  The 
other  parts  remain  subterranean. 

(3)  The  root. — The  primary  root  organized  by  one  of 
the  quadrants  of  the  embryo  is  a  temporary  affair  (Figs. 


PTERIDOPIIYTES  139 

111,  119),  as  it  is  in  an  unfavorable  position  in  reference  to 
the  dorsiventral  stem,  Avhich  puts  out  a  series  of  more  favor- 
ably placed  secondary  roots  into  the  soil  (Fig.  118).  The 
mature  leafy  sporophyte,  therefore,  has  neither  foot  nor 
primary  root,  the  product  of  two  of  the  quadrants  of  the 
embryo  having  disappeared. 

The  secondary  roots  put  out  by  the  stem  are  small,  and 
do  not  organize  an  extensive  system,  but  they  are  interest- 
ing as  representing  the  first  appearance  of  true  roots,  which 
therefore  come  in  with  the  vascular  system.  In  the  lower 
groups  the  root  function  of  absorption  is  not  assumed  by 
any  special  organ,  unless  rhizoids  sometimes  absorb ;  but 
true  roots  are  complex  in  structure  and  contain  vessels. 

(3)  The  stem. — In  most  of  the  Ferns  the  stem  is  sub- 
terranean and  dorsiventral  (Fig.  118),  but  in  the  "tree 
ferns  "  of  the  tropics  it  forms  an  erect,  aerial  shaft  bearing 
a  crown  of  leaves  (Fig.  120).  In  the  other  groups  of  Pteri- 
dophytes  there  are  also  aerial  stems,  both  erect  and  pros- 
trate. The  stem  is  complex  in  structure,  the  cells  being 
organized  into  different  "tissue  systems,"  prominent  among 
which  is  the  vascular  system.  These  tissue  systems  of  vas- 
cular plants  are  described  in  Chapter  XV. 

The  appearance  of  the  vascular  system  in  connection 
with  the  leafy  sporophyte  is  worthy  of  note.  The  leaves 
are  special  organs  for  chlorophyll  work,  and  must  receive 
the  raw  material  from  air  and  soil  or  water.  The  leaves 
of  the  moss  gametophyte  are  very  small  and  simple  affairs, 
and  can  be  supplied  with  material  by  using  very  little  ap- 
paratus. In  the  leafy  sporophyte,  however,  the  leaves  are 
very  prominent  structures,  capable  of  doing  a  great  deal 
of  work.  To  such  working  structures  material  must  be 
brought  rapidly  in  quantity,  and  manufactured  food  ma- 
terial must  be  carried  away,  and  therefore  a  special  con- 
ducting apparatus  is  needed.  This  is  supplied  by  the  vas- 
cular system.  These  vessels  extend  continuously  from  root- 
tips,  through  the  stem,  and  out  into  the  leaves,  where  they 


FiQ.  120.  A  group  of  tropical  plants.  To  the  left  of  the  center  is  a  tree  fern,  with  its 
slender  columnar  stem  and  crown  of  large  leaves.  The  large-leaved  plants  to  the 
right  are  bananas  (Monocotyledons).— From  "  Plant  Eelations." 


PTEKIDOPHYTES 


141 


are  spoken  of  as  ''leaf  veins."  Large  working  leaves  and 
a  vascular  system,  therefore,  belong  together  and  appear 
together;  and  the  vascular  plants  are  also  the  plants  with 
leafy  sporophytes. 

(4)  The  leaf. — Leaves  are  devices  for  spreading  out 
green  tissue  to  the  light,  and  in  the  Ferns  they  are  usually 
large.  There  is  a  stalk-like  portion  (petiole)  which  rises 
from  the  subterranean  stem,  and  a  broad  expanded  portion 
(blade)  exposed  to  the  light  and  air  (Fig.  118).  In  Ferns 
the  blade  is  usually  much  branched,  being  cut  up  into 
segments  of  various  sizes  and  forms. 

The  essential  structure  consists  of  an  expansion  of 
green  tissue  (mesophi/Il),  through  which  strands  of  the 
vascular  system  (veins)  branch,  forming  a  supporting 
framework,  and  over  all  a  compact  layer  of  protecting 
cells  (epidermis).  A  surface 
view  of  the  epidermis  shows 
that  it  is  pierced  by  numer- 
ous peculiar  pores,  called 
stomata,  meaning  "  mouths." 
The  surface  view  of  a  stoma 
shows  two  crescentic  cells 
(guard  cells)  in  contact  at 
the  ends  and  leaving  be- 
tween them  a  lens-shaped 
opening  (Fig.  121). 

A  cross-section  through 
a  leaf  gives  a  good  view  of 
the  three  regions  (Fig.  122). 
Above  and  below  is  the  col- 
orless epidermis,  pierced 
here  and  there  by  stomata ; 
between  the  epidermal  lay- 
ers the  cells  of  the  mesophyll  are  packed ;  and  among 
the  mesophyll  cells  there  may  be  seen  here  and  there  the 
cut  ends  of  the  veins.     The  leaf  is  usually  a  dorsiventral 


Fig.  121.  Some  epidermal  cells  froin 
leaf  of  Pteris,  showing  the  inter- 
locking walLs  and  three  stomata,  the 
guard  cells  containing  chloroplasts. 
— Land. 


142 


PLANT   STRUCTURES 


organ,  its  two  surfaces  being  differently  related  to  light. 
To  this  different  relation  the  mesophyll  cells  respond  in 
their  arrangement.  Those  in  contact  with  the  upper  epi- 
dermis become  elongated  and  set  endwise  close  together, 
forming  the  palisade  tissue;  those  below  are  loosely  ar- 


Fio.  122.  Cross-seclion  through  a  portion  of  the  leaf  of  Pteris,  showing  the  heavy- 
walled  epidermis  above  and  below,  two  stomata  in  the  lower  epidermis  (one  on 
each  side  of  the  center)  opening  into  intercellular  passages,  the  mesophyll  cells 
containing  chloroplasts,  the  upper  row  arranged  in  palisade  fashion,  the  other 
cells  loosely  arranged  (spongy  mesophyll)  and  leaving  large  intercellular  passages, 
and  in  the  center  a  section  of  a  veinlet  (vascular  bundle),  the  xylem  being  repre- 
sented by  the  central  group  of  heavy-walled  cells. — Land. 


ranged,  leaving  numerous  intercellular  spaces,  forming 
the  spongy  tissue.  These  spaces  form  a  system  of  inter- 
cellular passageways  among  the  working  mesophyll  cells, 
putting  them  into  communication  with  the  outer  air 
through  the  stomata.    The  freedom  of  this  communication 


PTERIDOPHYTES  143 

is  regulated  by  the  guard  cells  of  the  stomata,  which  come 
together  or  shrink  apart  as  occasion  requires,  thus  dimin- 
ishing or  enlarging  the  opening  between  them.  The  sto- 
mata have  well  been  called  "automatic  gateways  "  to  the 
system  of  intercellular  passageways. 

One  of  the  peculiarities  of  ordinary  fern  leaves  is 
that  the  vein  system  branches  dichotomously,  the  forking 
veins  being  very  conspicuous  (Figs.  133-126).  Another 
fern  habit  is  that  the  leaves  in  expanding  seem  to  unroll 
from  the  base,  as  though  they  had  been  rolled  from  the 
apex  downward,  the  apex  being  in  the  center  of  the  roll 
(Fig.  118).  This  habit  is  spoken  of  as  circinate,  from  a 
word  meaning  '^ circle"  or  "coil,"  and  circinate  leaves 
when  unrolling  have  a  crozier-like  tip.  The  arrangement 
of  leaves  in  bud  is  called  vernation  ("spring  condition"), 
and  therefore  the  Ferns  are  said  to  have  circinate  verna- 
tion. The  combination  of  dichotomous  venation  and  cir- 
cinate vernation  is  very  characteristic  of  Ferns. 

80.  Sporangia. — Among  Thallophytes  sporangia  are  usu- 
ally simple,  mostly  consisting  of  a  single  mother  cell ;  among 
Bryophytes  simple  sporangia  do  not  exist,  and  in  connec- 
tion with  the  usually  complex  capsule  of  the  sporogonium 
the  name  is  dropped ;  but  among  Pteridophytes  distinct 
sporangia  again  appear.  They  are  not  simple  mother  cells, 
but  many-celled  bodies.  Their  structure  varies  in  different 
groups  of  Pteridophytes,  but  those  of  ordinary  Ferns  may 
be  taken  as  an  illustration. 

The  sporangia  are  borne  by  the  leaves,  generally  upon 
the  under  surface,  and  are  usually  closely  associated  with 
the  veins  and  organized  into  groups  of  definite  form,  known 
as  sori.  A  sorus  may  be  round  or  elongated,  and  is  usually 
covered  by  a  delicate  flap  {indu^ium)  which  arises  from  the 
epidermis  (Figs.  118,  123,  124).  Occasionally  the  sori  are 
extended  along  the  under  surface  of  the  margin  of  the  leaf, 
as  in  maidenhair  fern  {Adiantnm),  and  the  common  brake 
{Pteris),  in  which  case  they  are  protected  by  the  inrolled 


1^  -m»oM44 


Fig.  123.  Fragrant  shield  fern  (A«/wc?- 
ium  frar/rans),  showing  general 
habit,  and  to  the  left  (a)  the  under 
surface  of  a  leaflet  bearing  sori 
covered  by  shield-like  indusia.— 
After  Marion  Satterlee. 


Fig.  124.  The  bladder  fern  (Cystoiiteris  bulb- 
ifera),  showing  general  habit,  and  to  the 
right  (a)  the  under  surface  of  a  leaflet, 
showing  the  dichotomous  venation,  and 
five  sori  protected  by  pouch-like  indusia. 
—After  Marion  Satterlee. 


PTERIDOPHYTES 


145 


margin  (Figs.  125,  126),  which  may  be  called  a  "false  in- 
dnsium." 

It  is  evident  that  such  leaves  are  doing  two  distinct 
kinds  of  work — clilorophyll  work  and  sj)ore  formation. 
This  is  true  of  most  of  the  ordinary  Ferns,  but  some  of 
them  show  a  tendency  to  di- 
vide the  work.  Certain  leaves, 
or  certain  leaf-branches,  pro- 
duce spores  and  do  no  chloro- 
phyll work,  while  others  do 
chlorophyll  work  and  produce 
no  spores.  This  differentia- 
tion in  the  leaves  or  leaf-re- 
gions is  indicated  by  appro- 
priate names.  Those  leaves 
which  jDroduce  only  spores  are 
called  sporo2JhijlU,  meaning 
"spore  leaves,"  while  the  leaf 
branches  thus  set  apart  are 
called  sporophyll  branches. 
Those  leaves  which  only  do 
chlorophyll  work  are  called /o- 
liage  leaves  ;  and  such  branch- 
es are  foliage  branches.  As 
sporophylls  are  not  called  upon 
for  chlorophyll  work  they  often 
become  much  modified,  being  much  more  compact,  and  not 
at  all  resembling  the  foliage  leaves.  Such  a  differentiation 
may  be  seen  in  the  ostrich  fern  and  sensitive  fern  ( Onoclea) 
(Figs.  127,  128),  the  climbing  fern  {Lygodium),  the  royal 
fern  {Osmunda),  the  moonwort  {Botrychium)  (Fig.  129), 
and  the  adder's  tongue  {Ophioglossiim)  (Fig.  130). 

An  ordinary  fern  sporangium  consists  of  a  slender  stalk 
and  a  bulbous  top  wliich  is  the  spore  case  (Fig.  118,  6). 
This  case  has  a  delicate  wall  formed  of  a  single  layer  of 
cells,  and  extending  around  it  from  the  stalk  and  nearly  to 


Fig.  12.5.  Leaflets  of  two  common 
ferns :  A,  the  common  brake 
(Pteris) ;  B,  maidenhair  (Adian- 
finii) ;  both  showing  sori  borne 
at  the  margin  and  protected  by 
the  infolded  margin,  which  thus 
forms  a  false  indusium. — Cald- 
well. 


146 


PLANT   STEUCTUKES 


the  stalk  again,  like  a  meridian  line  about  a  globe,  is  a  row  of 
peculiar  cells  with  thick  walls,  forming  a  heavy  ring,  called 
the  mimdus.  The  annulus  is  like  a  bent  spring,  and  when 
the  delicate  wall  becomes  yielding  the  spring  straightens 
violently,  the  wall  is  torn,  and  in  the  recoil  the  spores  are 
discharged  with  considerable  force  (Fig.  131).     This  dis- 


FiG.  126.— The  purple  cliflf  brake  (Pelhva  atropui-purea),  showing  general  habit,  and 
at  a  a  single  leaflet  showing  the  dichotomons  venation  and  the  infolded  margin 
covering  the  sori. — After  Marion  Satterlee. 

charge  of  fern  spores  may  be  seen  by  placing  some  sporangia 
upon  a  moist  slide,  and  under  a  low  power  watching  them 
as  they  dry  and  burst. 

Within  this  sporangium  the  archesporium  (see  §  66) 
consists  of  a  single  cell,  which  by  division  finally  produces 


PTERIDOniYTES 


147 


numerous  mother  cells,  in  each  of  which  a  tetrad  of  spores 
is  formed.     The  disorganization  of  the  walls  of  the  mother 


Fig.  127 


The  ostrich  (eTn(Onoclea  stnithiopteris),  showing  differentiation  of  foliage 
leaf  (a)  and  sporophyll  (6).— After  Marion  Satterlee. 


cells  sets  the  spores  free  in  the  cavity  of  the  sporangium, 
and  ready  for  discharge. 


Fig.  128.    The  sensitive  lern  (Otioclea  sensibilin).  sliowing  differentiation  of  foliage 
leaves  and  sporophylls.— From  "Field,  Forest,  and  Wayside  Flowers." 


PTEEIDOPIIYTES 


149 


Among  the  Bryophytes  the  sporogenous  tissue  appears 
very  early  in  the  development  of  the  sporogonium,  the  pro- 
duction of  spores  being  its  only  function ;  also  there  is  a 


^ 


Pig.  129.  A  nioonwort  (BotnjcM- 
ttm),  showing  the  leaf  differen- 
tiated into  foliage  and  sporophyll 
branches. — After  Strasburger. 

28 


Fig.  130.  The  adder's  tongue  {Ophioglossum 
■vulgatuni),  showing  two  leaves,  each 
with  a  foliage  branch  and  a  much  longer 
sporophyll  branch. — After  Marion  Sat- 

TERLEE. 


150 


PLANT   STRUCT ORES 


tendency  to  restrict  the  sporogenous  tissue  and  increase  the 
sterile  tissue.  It  will  be  observed  that  with  the  introduc- 
tion of  the  leafy  sporophyte  among  the  Pteridophytes  the 
sporangia  appear  much  later  in  its  development,  sometimes 
not  appearing  for  several  years,  as  though   they   are   of 


"^^s     ^        %;j^ 


^  .^^^^ 


Fig.  131.  A  series  showing  the  dehiscence  of  a  fern  sporangium,  the  rupture  of  the 
wall,  the  straightening  and  bending  back  of  the  annulus,  and  the  recoil.— After 
Atkinson. 


secondary  importance  as  compared  with  chlorophyll  work  ; 
and  that  the  sporogenous  tissue  is  far  more  restricted,  the 
sporangia  forming  a  very  small  part  of  the  bulk  of  the 
sporophyte  body. 


PTERIDOPHYTES  151 

81.  Heterospory. — This  phenomenon  appears  first  among 
Pteridophytes,  but  it  is  not  characteristic  of  them,  being  en- 
tirely absent  from  the  true  Ferns,  which  far  outnumber  all 
other  Pteridophytes.  Its  cliief  interest  lies  in  the  fact  that 
it  is  universal  among  the  Spermatophytes,  and  that  it  rep- 
resents the  change  which  leads  to  the  appearance  of  that 
high  group.  It  is  impossible  to  understand  the  greatest 
group  of  plants,  therefore,  without  knowing  something 
about  heterospory.  As  it  begins  in  simple  fashion  among 
Pteridophytes,  and  is  probably  the  greatest  contribution 
they  have  made  to  the  evolution  of  the  plant  kingdom, 
unless  it  be  the  leafy  sporophyte,  it  is  best  explained  here. 

In  the  ordinary  Ferns  all  the  spores  in  the  sporangia 
are  alike,  and  when  they  germinate  each  spore  produces  a 
prothallium  upon  which  both  antheridia  and  archegonia 
appear.  It  has  been  remarked,  however,  that  some  pro- 
thallia  are  dioecious — that  is,  some  bear  only  antheridia 
and  others  bear  only  archegonia.  In  this  case  it  is  evident 
that  the  spores  in  the  sporangium,  although  they  may  ap- 
pear alike,  produce  different  kinds  of  prothallia,  which 
may  be  called  male  and  female,  as  each  is  distinguished  by 
the  sex  organ  which  it  produces.  As  archegonia  are  only 
produced  by  well-nourished  prothallia,  it  seems  fair  to  sup- 
pose that  the  larger  spores  will  produce  female  prothallia, 
and  the  smaller  ones  male  prothallia. 

This  condition  of  things  seems  to  have  developed  finally 
into  a  permanent  and  decided  difference  in  the  size  of  the 
spores,  some  being  quite  small  and  others  relatively  large, 
the  small  ones  producing  male  gametophytes  (prothallia 
with  antheridia),  and  the  large  ones  female  gametophytes 
(prothallia  with  archegonia).  When  asexual  spores  differ 
thus  permanently  in  size,  and  give  rise  to  gametophytes  of 
different  sexes,  we  have  the  condition  called  heterospory 
(''spores  different"),  and  such  plants  are  called  heterospo- 
rous  (Fig.  139).  In  contrast  with  heterosporous  plants, those 
in  which  the  asexual  spores  appear  alike  are  called  homos- 


152  PLANT  STRUCTUEES 

porous,  or  sometimes  isosporous,  both  terms  meaning 
"spores  similar."  The  corresponding  noun  form  is  honios- 
pory  or  isospory.  Bryophytes  and  most  Pteridophytes  are 
homosporous,  while  some  Pteridophytes  and  all  Spermato- 
phytes  are  heterosporous. 

It  is  convenient  to  distinguish  by  suitable  names  the 
two  kinds  of  asexual  spores  produced  by  the  sporangia  of 
heterosporous  plants  (Fig.  139).  The  large  ones  are  called 
megaspores,  or  by  some  writers  macrospores,  both  terms 
meaning  " large  spores";  the  small  ones  are  called  m/cro- 
spores,  or  "small  spores."  It  should  be  remembered  that 
megaspores  always  produce  female  gametophytes,  and  mi- 
crospores male  gametophytes. 

This  differentiation  does  not  end  with  the  spores,  but 
soon  involves  the  sporangia  (Fig.  139).  Some  sporangia 
produce  only  megaspores,  and  are  called  tnegasporatigia ; 
others  produce  only  microspores,  and  are  called  microspo- 
rangia.  It  is  important  to  note  that  while  microsporangia 
usually  produce  numerous  microspores,  the  megasporangia 
produce  much  fewer  megaspores,  the  tendency  being  to 
diminish  the  number  and  increase  the  size,  until  finally 
there  are  megasporangia  which  produce  but  a  single  large 
functioning  megaspore. 

The  differentiation  goes  still  further.  If  the  sporangia 
are  born  upon  sporophylls,  the  sporophylls  themselves  may 
differentiate,  some  bearing  only  megasporangia,  and  others 
only  microsporangia,  the  former  being  called  megasporo- 
phylls,  the  latter  microsporopliylls.  In  such  a  case  the 
sequence  is  as  follows  :  megasporophylls  produce  megaspo- 
rangia, which  produce  megaspores,  which  in  germination 
produce  the  female  gametophytes  (prothallia  with  archego- 
nia) ;  while  the  microsporophylls  produce  microsporangia, 
which  produce  microspores,  which  in  germination  produce 
male  gametophytes  (prothallia  with  antheridia). 

A  formula  may  indicate  the  life  history  of  a  heteros- 
porous plant.     The  formula  of  homosporous  plants  with 


PTERIDOPHYTES  I53 

alternation  of  generations  (Bryophytes  and  most  Pterido- 
phytes)  was  given  as  follows  (§  63)  : 

G=g>  0— S— 0— G=:8>  0— S— 0— Giz8>  0— S,  etc. 

In  the  case  of  heterosporous  plants  (some  Pteridophytes 
and  all  Spermatophytes)  it  would  be  modified  as  follows  : 
g=8> o-S=8=^=8>  0— Si=8:=S=8>  0— S,  etc. 

In  this  case  two  gametophytes  are  involved,  one  pro- 
ducing a  sperm,  the  other  an  egg,  which  fuse  and  form  the 
oospore,  which  in  germination  produces  the  sporophyte, 
which  produces  two  kinds  of  asexual  spores  (megaspores 
and  microspores),  which  in  germination  produce  the  two 
gametophytes  again. 

One  additional  fact  connected  with  heterospory  should 
be  mentioned,  and  that  is  the  great  reduction  of  the  gam- 
etophyte.  In  the  homosporous  ferns  the  spore  develops 
a  small  but  free  and  independent  prothallium  which  pro- 
duces both  sex  organs.  When  in  heterosporous  plants  this 
work  of  producing  sex  organs  is  divided  between  two  gam- 
etophytes they  become  very  much  reduced  in  size  and  lose 
their  freedom  and  independence.  They  are  so  small  that 
they  do  not  escape  entirely,  if  at  all,  from  the  embrace  of 
the  spores  which  produce  them,  and  are  mainly  dependent 
for  their  nourishment  upon  the  food  stored  up  in  the  spores 
(Figs.  140,  141).  As  the  spore  is  produced  by  the  sporo- 
phyte, heterospory  brings  about  a  condition  in  which  the 
gametophyte  is  dependent  upon  the  sporoi3hyte,  an  exact 
reversal  of  the  condition  in  Bryophytes. 

The  relative  importance  of  the  gametophyte  and  the 
sporophyte  throughout  the  plant  kingdom  may  be  roughly 
indicated  by  the   accompanying   diagram,  in   which   the 


shaded  part  of  the  parallelogram  represents  the  gameto- 
phyte and  the  unshaded  part  the  sporophyte.     Among  the 


]^54  PLANT   STKUCTUEES 

lowest  plants  the  gametophyte  is  represented  by  the  whole 
plant  structure.  When  the  sporophyte  first  appears  it  is 
dependent  upon  the  gametophyte  (some  Thallophytes  and 
the  Bryophytes),  and  is  relatively  inconspicuous.  Later 
the  sporophyte  becomes  independent  (most  Pteridophytes), 
the  gametophyte  being  relatively  inconspicuous.  Finally 
(heterosporous  Pteridophytes)  the  gametophyte  becomes 
dependent  upon  the  sporophyte,  and  in  Spermatophytes  is 
so  inconspicuous  and  concealed  that  it  is  only  observed  by 
means  of  laboratory  appliances,  while  the  sporophyte  is  the 
whole  plant  of  ordinary  observation. 


CHAPTER  X 

THE  GREAT  GROUPS  OF  PTERIDOPHYTES 

82.  The  great  groups.— At  least  three  independent  lines 
of  Pteridopliytes  are  recognized  :  (1)  Filicales  (Ferns), 
(2)  Equisetales  (Scouring  rushes,  Horsetails),  and  (3)  Ly- 
copodiahs  (Club-mosses).  The  Ferns  are  much  the  most 
abundant,  the  Club-mosses  are  represented  by  a  few  hun- 
dred forms,  while  the  Horsetails  include  only  about  twenty- 
five  species.  These  three  great  groups  are  so  unlike  that 
they  hardly  seem  to  belong  together  in  the  same  division 
of  the  plant  kingdom. 

Filicales  {Ferns) 

83.  General  characters.— The  Ferns  were  used  in  the 
preceding  chapter  as  types  of  Pteridophytes,  so  that  little 
need  be  added.  They  well  deserve  to  stand  as  types,  as 
they  contain  about  four  thousand  of  the  four  thousand  five 
hundred  species  belonging  to  Pteridophytes.  Although 
found  in  considerable  numbers  in  temperate  regions,  their 
chief  display  is  in  the  tropics,  where  they  form  a  striking 
and  characteristic  feature  of  the  vegetation.  In  the  trop- 
ics not  only  are  great  masses  of  the  low  forms  to  be  seen, 
from  those  with  delicate  and  filmy  moss  like  leaves  to  those 
with  huge  leaves,  but  also  tree  forms  with  cylindrical 
trunks  encased  by  the  rough  remnants  of  fallen  leaves  and 
sometimes  rising  to  a  height  of  thirty-five  to  forty-five 
feet,  with  a  great  crown  of  leaves  fifteen  to  twenty  feet 
long  (Fig.  120). 

155 


THE  GKEAT  GROUPS  OF  PTERIDOPHYTES      I57 

There  are  also  epiphytic  forms  (air  plants) — that  is, 
those  which  perch  "  upon  other  plants "  but  derive  no 
nourishment  from  them  (Fig.  112).  This  habit  belongs 
chiefly  to  the  warm  and  moist  tropics,  where  the  plants 
can  absorb  sufficient  moisture  from  the  air  without  send- 
ing roots  into  the  soil.  In  this  way  many  of  the  tropical 
ferns  are  found  growing  upon  living  and  dead  trees  and 
other  plants.  In  the  temperate  regions  the  chief  ejai- 
phytes  are  Lichens,  Liverworts,  and  Mosses,  the  Ferns  be- 
ing chiefly  found  in  moist  woods  and  ravines  (Fig.  133), 
although  a  number  grow  in  comparatively  dry  and  exposed 
situations,  sometimes  covering  extensive  areas,  as  the  com- 
mon brake  (Pteris)  (Fig.  125). 

The  Filicales  differ  from  the  other  groups  of  Pterido- 
phytes  chiefly  in  having  few  large  leaves,  which  do  chloro- 
phyll work  and  bear  sporangia.  In  a  few  of  them  there  is  a 
differentiation  of  functions  in  foliage  branches  and  sporo- 
phyll  branches  (Figs.  127-130),  but  even  this  is  excep- 
tional. Another  distinction  is  that  the  stems  are  un- 
branched. 

84.  Origin  of  sporangia. — An  important  feature  in  the 
Ferns  is  the  origin  of  the  sporangia.  In  some  of  them  a 
sporangium  is  developed  from  a  single  epidermal  cell  of 
the  leaf,  and  is  an  entirely  superficial  and  generally  stalked 
affair  (Fig.  118,  5)  ;  in  others  the  sporangium  in  its  devel- 
opment involves  several  epidermal  and  deeper  cells  of  the 
leaf,  and  is  more  or  less  of  an  imbedded  affair.  In  the  first 
case  the  ferns  are  said  to  be  leptosporangiate  ;  in  the  sec- 
ond case  they  are  euspoi'angiate. 

The  leptosporangiate  Ferns  are  overwhelmingly  abun- 
dant as  compared  with  the  Eusporangiates.  Back  in  the 
Coal-measures,  however,  there  was  an  abundant  fern  vege- 
tation which  was  probably  all  eusporangiate.  The  Lep- 
tosporangiates  seem  to  be  the  modern  Ferns,  the  once 
abundant  Eusporangiates  being  represented  now  in  the 
temperate  regions  only  by  such  forms  as  moonwort  {Bo- 


158 


PLANT   STKUCTUKES 


trycliium)  (Fig.  129)  and  adder's  tongue  (OpMoglossiim) 
(Fig.  130).  It  is  important  to  note,  however,  that  the 
Horsetails  and  Club-mosses  are  Eusporangiates,  as  well  as 
all  the  Seed-plants. 

Another  small  but  interesting  group  of  Ferns  includes 
the  ''Water-ferns,"  floating  forms  or  sometimes  on  muddy 
flats.     The  common  Marsilia  may  be  taken  as  a  type  (Fig. 

133).  The  slender  creeping  stem 
sends  down  numerous  roots  into 
the  mucky  soil,  and  at  intervals 
gives  rise  to  a  comparatively  large 
leaf.  This  leaf  has  a  long  erect 
petiole  and  a  blade  of  four  spread- 


r^  r^ 


Fig.  133.— a  water-fern  {Marsilia), 
showing  horizontal  stem,  with 
descending  roots,  and  ascend- 
ing leaves ;  a,  a  young  leaf 
showing  circinate  vernation ; 
s,s,  sporophy  1 1  branches  ( "  spo- 
rocarps  "). — After  Bischoff. 


A       '  '   '      J? 

Fig.  134.  One  of  the  floating  water-ferns  (Sal- 
vinia),  showing  side  view  (^4)  and  view  from 
above  (B).  The  dangling  root-like  processes 
are  the  modified  submerged  leaves.  In  A, 
near  the  top  of  the  cluster  of  submerged 
leaves,  some  sporophyll  branches  ("sporo- 
carps")  may  be  seen. — After  Bischoff. 


ing  wedge-shaped  leaflets  like  a  "  four-leaved  clover. "  The 
dichotomous  venation  and  circinate  vernation  at  once  sug- 
gest the  fern  alliance.     From  near  the  base  of  the  petiole 


THE  GREAT  GROUPS  OF  PTERIDOPHYTES      159 

another  leaf  branch  arises,  in  which  the  blade  is  modified 
as  a  sporophyll.  In  this  case  the  sporophyll  incloses  the 
sporangia  and  becomes  hard  and  nut-like.  Another  com- 
mon form  is  the  floating  Salvinia  (Fig.  134).  The  chief 
interest  lies  in  the  fact  that  the  water-ferns  are  heteros- 
porous.  As  they  are  leptosporangiate  they  are  thought 
to  have  been  derived  from  the  ordinary  leptosporangiate 
Ferns,  which  are  homosporous. 

Three  fern  groups  are  thus  outlined  :  (1)  homosporous- 
eusporangiate  forms,  now  almost  extinct ;  (2)  homosporous- 
leptosporangiate  forms,  the  great  overwhelming  modern 
group,  not  only  of  Filicales  but  also  of  Pteridophytes,  well 
called  true  Ferns,  and  thought  to  be  derived  from  the  pre- 
ceding group ;  and  (3)  heterosporous-leptosporangiate 
forms,  the  water-ferns,  thought  to  be  derived  from  the  pre- 
ceding group. 

Equisetales  ( Horsetails  or  Scouring  rushes) 

85.  General  characters. — The  twenty-five  forms  now  rep- 
resenting this  great  group  belong  to  a  single  genus  {Equise- 
tum,  meaning  "horsetail"),  but  they  are  but  the  linger- 
ing remnants  of  an  abundant  flora  which  lived  in  the  time 
of  the  Coal-measures,  and  helped  to  form  the  forest  vegeta- 
tion. The  living  forms  are  small  and  inconspicuous,  but 
very  characteristic  in  appearance.  They  grow  in  moist  or 
dry  places,  sometimes  in  great  abundance  (Fig.  135). 

The  stem  is  slender  and  conspicuously  Jointed,  the  joints 
separating  easily ;  it  is  also  green  and  fluted  with  small 
longitudinal  ridges  ;  and  there  is  such  an  abundant  deposit 
of  silica  in  the  epidermis  that  the  plants  feel  rough.  This 
last  property  suggested  its  former  use  in  scouring,  and  its 
name  "  scouring  rush."  At  each  joint  is  a  sheath  of  minute 
leaves,  more  or  less  coalesced,  the  individual  leaves  some- 
times being  indicated  only  by  minute  teeth.  This  arrange- 
ment of  leaves  in  a  circle  about  the  joint  is  called  the  cyclic 


Fig.  135.  Equisetian  arvense,  a  common  horsetail:  1.  three  fertile  shoots  rising  from 
the  dorsiventral  stem,  showing  the  cycles  of  coalesced  scale-leaves  at  the  joints 
and  the  terminal  strobili  with  numerous  sporophylls,  that  at  a  being  mature;  2, 
a  sterile  shoot  from  the  same  stem,  showing  branching;  3,  a  single  peltate  sporo- 
phyll  bearing  sporangia;  A,  view  of  sporophyll  from  beneath,  showing  dehiscence 
of  sporangia;  5,  6,  7.  spores,  showing  the  unwinding  of  the  outer  coat,  which  aids 
in  dispersal.— After  Wossidlo. 


THE   GREAT  GROUPS   OF   PTERIDOPIIYTES 


IGl 


arrangement,  or  sometimes  the  luliorUd  arrangement,  each 
such  set  of  leaves  being  called  a  cycle  or  a  ivhorl.  These 
leaves  contain  no  chlorophyll  and  have  evidently  abandoned 
chlorophyll  work,  which  is  carried  on  by  the  green  stem. 
Such  leaves  are  known  as  scales,  to  distinguish  them  from 
foliage  leaves.  The  stem  is  either  simple  or  profusely 
branched  (Fig.  135). 

86.  The  strobilus. — One  of  the  distinguishing  characters 
of  the  group  is  that  chlorophyll-work  and  spore-formation 
are  completely  difEerentiated.     Although  the  foliage  leaves 


Dioecious  gametophytes  of  Eqmsetvm ;  A,  the  female  gametophyte,  show- 
branching,  i-hizoids.  and  an  archegonium  (ar);  B,  the  male  gametophyte, 

IPriflifl    i  i^    \   A  f  f  Pr    P  iTVT-P'RWT  T. 


uig  orancning,  rnizoias.  ana  an  arcnegonium  (ar) 
showing  several  antheridia  (  6  ).— After  Campbell. 


are  reduced  to  scales,  and  the  chlorophyll-work  is  done  by 
the  stem,  there  are  well-organized  sporophylls.  The  sporo- 
phylls  are  grouped  close  together  at  the  end  of  the  stem  in 
a  compact  conical  cluster  which  is  called  a  sfrohihn^,  the 
Latin  name  for  "pine  cone,"  which  this  cluster  of  sporo- 
phylls resembles  (Fig.  135). 

Each  sporophyll  consists  of  a  stalk-like  portion  and  a 
shield-like  {peltate)  top.      Beneath  the  shield  hang  the 


162  PLANT   STKUCTURES 

sporangia,  which  produce  spores  of  but  one  kind,  hence 
these  plants  are  homosporous  ;  and  as  the  sporangia  origi- 
nate in  eusporangiate  fashion,  Eqvisetum  has  the  homospo- 
rous-eusporangiate  combination  shown  by  one  of  the  Fern 
groups.  It  is  interesting  to  know,  however,  that  some  of 
the  ancient,  more  highly  organized  members  of  this  group 
were  heterosporous,  and  that  the  present  forms  have 
dioecious  gametophytes  (Fig.  136). 

Lycopodiales  {Cluh-mosses) 

87.  General  characters. — This  group  is  now  represented 
by  about  five  hundred  species,  most  of  which  belong  to 
the  two  genera  Lt/copodiiim  and  Selagmella,  the  latter 
being  much  the  larger  genus.  The  plants  have  slender, 
branching,  prostrate,  or  erect  stems  completely  clothed 
with  small  foliage  leaves,  having  a  general  moss-like 
appearance  (Fig.  137).  Often  the  erect  branches  are 
terminated  by  conspicuous  conical  or  cylindrical  strobili, 
which  are  the  "  clubs  "  that  enter  into  the  name  "  Club- 
mosses."  There  is  also  a  certain  kind  of  resemblance 
to  miniature  pines,  so  that  the  name  "  Ground-pines  "  is 
sometimes  used. 

Lycopodiales  were  once  much  more  abundant  than  now, 
and  more  highly  organized,  forming  a  conspicuous  part  of 
the  forest  vegetation  of  the  Coal-measures. 

One  of  the  distinguishing  marks  of  the  group  is  that  the 
sperm  does  not  resemble  that  of  the  other  Pteridophytes, 
but  is  of  the  Bryophyte  type  (Fig.  140,  F).  That  is,  it 
consists  of  a  small  body  with  two  cilia,  instead  of  a  large 
sj^irally  coiled  body  with  many  cilia.  Another  distinguish- 
ing character  is  that  there  is  but  a  single  sporangium  pro- 
duced by  each  sporophyll  (Fig.  137).  This  is  in  marked 
contrast  with  the  Filicales,  whose  leaves  bear  very  numer- 
ous sporangia,  and  with  the  Equisetales,  whose  sporophylls 
bear  several  sporangia. 


THE   GKEAT   GROCPS   OF   PTERIDOPllYTES 


163 


Fie.  137.  A  common  chib-moss  (LycopodXmn  clavatinn):  1,  the  whole  plant,  showing 
horizontal  stem  giving  rise  to  roots  and  to  erect  branches  bearing  strobili;  2,  a 
single  sporophyll  with  its  sporangium;  3,  spores,  much  magnified.— After  Wos- 

8IDLO. 


88.  Lycopodium. — This  genus  contains  fewer  forms  than 
the  other,  but  they  are  larger  and  coarser  and  more  charac- 
teristic of  the  temperate  regions,  being  the  ordinary  Club- 
mosses  (Fig,  137).  They  also  more  commonly  display 
conspicuous  and  distinct  strobili,  although  there  is  every 


164 


PLANT   STRUCTUKES 


gradation  between  ordinary  foliage  leaves  and  distinct 
sporophylls. 

The  sporangia  are  borne  either  by  distinct  sporophylls 
or  by  the  ordinary  foliage  leaves  near  the  summit  of  the 
stem.  At  the  base  of  each  of  these  leaves,  or  sporophylls, 
on  the  upper  side,  is  a  single  sporangium  (Fig.  137).  The 
sporangia  are  eusporangiate  in  origin,  and  as  the  spores  are 
all  alike,  Lycopodium  has  the  same  homosporous-eusporan- 
giate  combination  noted  in  Equisetales  and  in  one  of  the 
groups  of  Filicales. 

89.  Selaginella. — This  large  genus  contains  the  smaller, 
more  delicate  Club-mosses,  often  being  called  the  "  little 
Club-mosses."    They  are  especially  displayed  in  the  trop- 


Fia.  138.    Selaginella,  showing  general  epraylike  habit,  and  dangling  leafless  stems 
which  strike  root  (rAisopAores).— From  "  Plant  Relations." 


ics,  and  are  common  in  greenhouses  as  delicate,  mossy, 
decorative  plants  (Fig.  138).  In  general  the  sporophylls 
are  not  different  from  the  ordinary  leaves  (Fig.  139),  but 
sometimes  they  are  modified,  though  not  so  distinct  as  in 
certain  species  of  Lycopodium. 


THE   GREAT   GKOUrS   OF   rTEKIDOl'HYTES 


165 


The  solitary  sporangium  appears  in  the  axils  (upper 
angles  formed  by  tlie  leaves  with  the  stem)  of  the  leaves 
and  sporophylls,  but  arise  from  the  stem  instead  of  the 


Pig.  139.  Selaginella  Martensii :  A,  branch  bearing  strobili;  B,  a  microsporophyll 
with  a  microsporangiiim,  showing  microspores  through  a  rupture  in  the  wall;  C, 
a  megasporopliyll  with  a  megasporangium  ;  D,  megaspores  :  E,  microspores.— 

GOLDBERGER. 

29 


166 


PLANT   STRUCTDRES 


leaf  (Fig.  139).  This  is  important  as  showing  that  sporan- 
gia may  be  produced  by  stems  as  well  as  by  leaves,  those 
being  produced  by  leaves  being  called  foliar,  and  those  by 
stem  cauUne. 

The  most  important  fact  in  connection  with  Selaginella, 
however,  is  that  it  is  heterosporous.  Megasporangia,  each 
usually  containing  but  four  megaspores,  are  found  in  the 
axils  of  a  few  of  the  lower  leaves  of  the  strobilus,  and  more 
numerous  microsporangia  occur  in  the  upjDer  axils,  con- 
taining very  many  microspores  (Fig.  139).  The  character 
of  the  gametophytes  of  heterosporous  Pteridophytes  may 
be  well  illustrated  by  those  of  Selaginella. 

The  microspore  germinates  and  forms  a  male  gameto- 
phyte  so  small  that  it  is  entirely  included  within  the  spore 


IV  j; 


Fig.  140.  Male  gametophyte  of  Selaginella :  in  each  case  p  is  the  prothallial  cell,  w 
the  wall  cells  of  the  antheridium,  s  the  sperm  tissue:  F,  the  biciliate  sperms. — 
After  Belajeff. 


wall  (Fig.  140).  A  single  small  cell  is  all  that  represents 
the  ordinary  cells  of  the  prothallium,  while  all  the  rest  is 
an  antheridium,  consisting  of  a  wall  of  a  few  cells  sur- 
rounding numerous  sperm  mother  cells.     In  the  presence 


THE  GREAT  GROUPS  OF  PTERIDOPHYTES 


167 


of  water  the  antheridium  wall  breaks  down,  as  also  do  the 
walls  of  the  mother  cells,  and  the  small  biciliate  sperms 
are  set  free. 

The  much  larger  megaspores  germinate  and  become 
filled  with  a  mass  of  numerous  nutritive  cells,  representing 
the  ordinary  cells  of  a  prothallium  (Fig.  141).  The  spore 
wall  is  broken  by  this  growing  prothallium,  a  part  of  which 
thus  protrudes  and  becomes  exposed,  although  the  main 
part  of  it  is  still  invested  by  the  old  megaspore  wall.  In 
this    exposed    portion 

of  the  female  gameto-  |i  \]       ^     ^^ 

phyte  the  archegonia 
appear,  and  thus  be- 
come accessible  to  the 
sperms.  In  the  case 
of  Isoetes  (see  §  90) 
the  reduction  of  the 
female  gametophyte  is 
even  greater,  as  it  does 
not  project  from  the 
megaspore  wall  at  all, 
and  the  archegonia 
are  made  accessible 
through  cracks  in  the 
wall  immediately  over 
them. 

The  embryo  of  Se- 
laginella  is  also  impor- 
tant to  consider.  Be- 
ginning its  development  in  the  venter  of  the  archegonium, 
it  first  lies  upon  the  exposed  margin  of  the  prothallium, 
while  the  mass  of  nutritive  cells  lie  deep  within  the  mega- 
spore (Fig.  141,  e7nh^,  emh^).  It  first  develops  an  elongated 
cell,  or  row  of  cells,  which  thrusts  the  embryo  cell  deeper 
among  the  nutritive  cells.  This  cell  or  row  of  cells,  formed 
by  the  embryo  to  place  the  real  embryo  cell  in  better  rela- 


spm 


Fio.  141.  YemaXe  gn.n\eto\^\\yte  oi  a.  Selagiriella : 
spm,  wall  of  megaspore  ;  pr.  gametophyte ; 
ar,  an  archegonium  ;  einb^  and  emb^.  em- 
bryo .s])orophyte8  ;  et.  suspensors  ;  the  gam- 
etophyte has  developed  a  few  rhizoids. — 
After  Pfeffer. 


1G8 


PLANT   STKUCTUKES 


tion  to  its  food  supply,  is  called  the  suspe?isor,  and  is  a 
temporary  organ  of  the  embryo  (Figs.  141,  142,  et).  At 
the  end  of  the  snspensor  the  real  embryo  develops,  and 
when  its  regions  become  organized  it  shows  the  following 
parts  :  (1)  a  large  foot  buried  among  the  nutritive  cells  of 
the  prothallium  and  absorbing  nourishment ;  (2)  a  root 
stretching  out  toward  the  substratum  ;  (3)  a  stem  extend- 


FiG.  142.  Embryo  of  Selaginella  removed  from  the  gainetophyte,  showing  snspensor 
(et),  root-tip  («•),  foot  (/),  cotyledons  (W),  stem-lip  (st),  and  ligules  (lig).— After 
Pfeffer. 


ing  in  the  other  direction,  and  bearing  Just  behind  its  tip 
(4)  a  pair  of  opposite  leaves  (cotyledons)  (Fig.  142). 

As  the  sporangia  of  Selaginella  are  eusporangiate,  this 
genus  has  the  heterosporous-eusporangiate  combination — a 
combination  not  mentioned  heretofore,  and  being  of  special 
interest  as  it  is  the  combination  which  belongs  to  all  the 
Spermatophytes.  For  this  and  other  reasons,  Selaginella 
is  one  of  the  Pteridophyte  forms  which  has  attracted 
special  attention,  as  possibly  representing  one  of  the  an- 
cestral forms  of  the  Seed-plants. 


THE   GREAT  GROUPS   OF   PTERIDOPIIYTES 


109 


90.  Isoetes. — This  little  group  of  aquatic  plants,  known 
as  "quilhvorts,"  is  very  puzzling  as  to  its  relationships 
among  Pteridophytes.  By  some  it  is  put  with  the  Ferns, 
forming  a  distinct  division  of  Filicales  ;  by  others  it  is  put 


Fig.  143.  A  common  quillwort  (Isoetes  lacns- 
tris),  showing  cluster  of  roots  dichoto- 
mously  branching,  and  cluster  of  leaves 
each  enlarged  at  base  and  inclosing  a  sin- 
gle sporangium.— After  Schenck. 


Fig.  144.  Sperm  of  Isoetes,  show- 
ing spiral  body  and  seven  long 
cilia  arising  from  the  beak.— 
After  Belajefp. 


with  the  Club-mosses,  and  is  associated  with  Selaginella. 
It  resembles  a  bunch  of  fine  grass  growing  in  shoal  water 
or  in  mud,  but  the  leaves  enlarge  at  the  base  and  overlap 
one  another  and  the  very  short  tuberous  stem  (Fig.  143). 
Within  each  enlarged  leaf  base  a  single  sporangium  is 
formed,  and  the  cluster  contains  both  megasporangia  and 
microsporangia.  The  sporangia  are  eusporangiate,  and 
therefore  Isoetes  shares  with  Selaginella  the  distinction  of 


l^Q  PLANT   STRUCTURES 

having  the  heterosporous-eusporangiate  combination,  which 
is  a  feature  of  the  Seed-plants. 

The  embryo  is  also  peculiar,  and  is  so  suggestive  of  the 
embryo  of  the  Monocotyledons  (see  §  114)  among  Seed- 
plants  that  some  regard  it  as  possibly  representing  the 
ancestral  forms  of  that  group  of  Spermatophytes.  The 
peculiarity  lies  in  the  fact  that  at  one  end  of  the  axis  of  the 
embryo  is  a  root,  and  at  the  other  the  first  leaf  (cotyledon), 
while  the  stem  tip  rises  as  a  lateral  outgrowth.  This  is 
exactly  the  distinctive  feature  of  the  embryo  of  Monocoty- 
ledons. 

The  greatest  obstacle  in  the  way  of  associating  these 
quillworts  with  the  Club-mosses  is  the  fact  that  their  sperms 
are  of  the  large  and  spirally  coiled  multiciliate  type  which 
belongs  to  Filicales  and  Equisetales  (Fig.  144),  and  not  at 
all  the  small  biciliate  type  which  characterizes  the  Club- 
mosses  (Fig.  140).  To  sum  up,  the  short  unbranched  stem 
with  comparatively  few  large  leaves,  and  the  coiled  multi- 
ciliate sperm,  suggest  Filicales  ;  while  the  solitary  spo- 
rangia and  the  heterosporous-eusporangiate  character  sug- 
gest SeJagineUa. 


CHAPTEE    XI 

SPERMATOPHYTES :    GYMNOSPERMS 

91.  Summary  from  Pteridophytes. — In  considering  the 
important  contributions  of  Pteridophytes  to  the  evolution 
of  the  plant  kingdom  the  following  seem  worthy  of  note  : 

(1)  Prominence  of  sporophyte  and  development  of  vascu- 
lar system. — This  prominence  is  associated  with  the  display 
of  leaves  for  chlorophyll  work,  and  the  leaves  necessitate 
the  work  of  conduction,  which  is  arranged  for  by  the  vas- 
cular system.     This  fact  is  true  of  the  whole  group. 

(2)  Differentiation  of  sporopJtylls.— The  appearance  of 
sporophylls  as  distinct  from  foliage  leaves,  and  their  or- 
ganization into  the  cluster  known  as  the  strobilus,  are  facts 
of  prime  importance.  This  differentiation  appears  more  or 
less  in  all  the  great  groups,  but  the  strobilus  is  distinct  only 
in  Horsetails  and  Club-mosses. 

(3)  Introduction  of  heterospory  and  reduction  of  garnet o- 
phytes. — Heterospory  appears  independently  in  all  of  the 
three  great  groups — in  the  water-ferns  among  the  Fili- 
cales,  in  the  ancient  horsetails  among  the  Equisetales,  and 
in  Selaginella  and  Isoetes  among  Lycopodiales.  All  the 
other  Pteridophytes,  and  therefore  the  great  majority  of 
them,  are  homosporous.  The  importance  of  the  appear- 
ance of  heterospory  lies  in  the  fact  that  it  leads  to  the 
development  of  Spermatophytes,  and  associated  with  it  is 
a  great  reduction  of  the  gametophytes,  which  project  little, 
if  at  all,  from  the  spores  which  produce  them. 

92.  Summary  of  the  four  groups.— It  may  be  well  in  this 
connection  to  give  certain  prominent  characters  which  will 

171 


1^2  PLANT  STRUCTURES 

serve  to  distinguish  the  four  great  groups  of  plants.  It 
must  not  be  supposed  that  these  are  the  only  characters, 
or  even  the  most  important  ones  in  every  case,  but  they 
are  convenient  for  our  purpose.  Two  characters  are  given 
for  each  of  the  first  three  groups — one  a  positive,  character 
which  belongs  to  it,  the  other  a  negative  character  which 
distinguishes  it  from  the  group  above,  and  becomes  the 
positive  character  of  that  group. 

(1)  Tliallojjhytes. — Thallus  body,  but  no  archegonia. 

(2)  Bryoiiliytes. — Archegonia,  but  no  vascular  system. 

(3)  Pteridophytes. — Vascular  system,  but  no  seeds. 

(4)  Sjmrmatojjltytes. — Seeds. 

93.  General  characters  of  Spermatophytes. — This  is  the 
greatest  group  of  plants  in  rank  and  in  display.  So  con- 
spicuous are  they,  and  so  much  do  they  enter  into  our 
experience,  that  they  have  often  been  studied  as  "botany," 
to  the  exclusion  of  the  other  groups.  The  lower  groups 
are  not  meiely  necessary  to  fill  out  any  general  view  of  the 
plant  kingdom,  but  they  are  absolutely  essential  to  an 
understanding  of  the  structures  of  the  highest  group. 

This  great  dominant  group  has  received  a  variety  of 
names.  Sometimes  they  are  called  Antliopliytes,  meaning 
"Flowering  plants,"  with  the  idea  that  they  are  distin- 
guished by  the  production  of  "flowers."  A  flower  is  diffi- 
cult to  define,  but  in  the  popular  sense  all  Spermatophytes 
do  not  produce  flowers,  while  in  another  sense  the  strobilus 
of  Pteridophytes  is  a  flower.  Hence  the  flower  does  not 
accurately  limit  the  group,  and  the  name  Anthophytes  is 
not  in  general  use.  Much  more  commonly  the  group  is 
called  Phanerogams  (sometimes  corrupted  into  Phgenogams 
or  even  Phenogams),  meaning  "  evident  sexual  reproduc- 
tion." At  the  time  this  name  was  proposed  all  the  other 
groups  were  called  Cryptogams,  meaning  "hidden  sexual 
reproduction."  It  is  a  curious  fact  that  the  names  ought 
to  have  been  reversed,  for  sexual  reproduction  is  much  more 
evident  in  Cryptogams  than  in  Phanerogams,  the  mistake 


SPKRMATOPIIYTES:   GYMNOSPEKMS  1^3 

arising  from  the  fact  that  what  were  supposed  to  be  sexual 
organs  in  Phanerogams  have  proved  not  to  be  such.  The 
name  Phanerogam,  therefore,  is  being  generally  abandoned  ; 
but  the  name  Cryptogam  is  a  useful  one  when  the  lower 
groups  are  to  be  referred  to  ;  and  the  Pteridophytes  are 
still  very  frequently  called  the  Vascular  Cryptogams.  The 
most  distinguishing  mark  of  the  group  seems  to  be  the 
production  of  seeds,  and  hence  the  name  Spermatojjhytes, 
or  "  Seed-plants,"  is  coming  into  general  use. 

The  seed  can  be  better  defined  after  its  development 
has  been  described,  but  it  results  from  the  fact  that  in  this 
group  the  single  megaspore  is  never  discharged  from  its 
megasporangium,  but  germinates  just  where  it  is  devel- 
oped. The  great  fact  connected  with  the  group,  therefore, 
is  the  retention  of  the  megaspore,  which  results  in  a  seed. 
The  full  meaning  of  this  will  appear  later. 

There  are  two  very  independent  lines  of  Seed-plants, 
the  Gymnospenns  and  the  Angiosperfiis.  The  first  name 
means  "naked  seeds,"  referring  to  the  fact  that  the  seeds 
are  always  exposed  ;  the  second  means  "  inclosed  seeds," 
as  the  seeds  are  inclosed  in  a  seed  vessel. 

Gymnosperms 

94.  General  characters. — The  most  familiar  Gymnosperms 
in  temperate  regions  are  the  pines,  spruces,  hemlocks, 
cedars,  etc.,  the  group  so  commonly  called  ''evergreens." 
It  is  an  ancient  tree  group,  for  its  representatives  were 
associated  with  the  giant  club-mosses  and  horsetails  in 
the  forest  vegetation  of  the  Coal-measures.  Only  about 
four  hundred  species  exist  to-day  as  a  remnant  of  its  for- 
mer disjilay,  although  the  pines  still  form  extensive  forests. 
The  group  is  so  diversified  in  its  structure  that  all  forms 
can  not  be  included  in  a  single  description.  The  common 
pine  {Pinns),  therefore,  will  be  taken  as  a  type,  to  show 
the  general  Gymnosperm  character. 


]^74  PLANT   STRUCTURES 

95.  The  plant  body. — The  great  body  of  the  plant,  often 
forming  a  large  tree,  is  the  sporophyte ;  in  fact,  the 
gametophytes  are  not  visible  to  ordinary  observation.  It 
should  be  remembered  that  the  sporophyte  is  distinctly  a 
sexless  generation,  and  that  it  develops  no  sex  organs. 
This  great  sporophyte  body  is  elaborately  organized  for 
nutritive  work,  with  its  roots,  stems,  and  leaves.  These 
organs  are  very  complex  in  structure,  being  made  up  of 
various  tissue  systems  that  are  organized  for  special  kinds 
of  work.  The  leaves  are  the  most  variable  organs,  being 
differentiated  into  three  distinct  kinds — (1)  foliage  leaves, 
(2)  scales,  and  (3)  sporophylls, 

96.  Sporophylls. — The  sporophylls  are  leaves  set  apart  to 
produce  sporangia,  and  in  the  pine  they  are  arranged  in 
a  strobilus,  as  in  the  Horsetails  and  Club-mosses.  As 
the  group  is  lieterosporous,  however,  there  are  two  kinds 
of  sporophylls  and  two  kinds  of  strobili.  One  kind  of 
strobilus  is  made  up  of  megasporophylls  bearing  mega- 
sporangia  ;  the  other  is  made  up  of  microsporophylls  bear- 
ing microsporangia.  These  strobili  are  often  spoken  of  as 
the  "  flowers  "  of  the  pine,  but  if  these  are  flowers,  so  are 
the  strobili  of  Horsetails  and  Club-mosses. 

97.  Microsporophylls. — In  the  pines  the  strobilus  com- 
posed of  microsporophylls  is  comparatively  small  (Figs. 
145,  fZ,  164).  Each  sporophyll  is  like  a  scale  leaf,  is  nar- 
rowed at  the  base,  and  upon  the  lower  surface  are  borne 
two  prominent  sporangia,  which  of  course  are  microspo- 
rangia, and  contain  microspores  (Fig.  146). 

These  structures  of  Seed-plants  all  received  names 
before  they  were  identified  with  the  corresponding  struc- 
tures of  the  lower  groups.  The  microsporophyll  was  called  a 
stamen,  the  microsporangia  ;;o/'?^^w-.S'acs,  and  the  microspores 
pollen  grains,  or  simply  pollen.  These  names  are  still  very 
convenient  to  use  in  connection  with  the  Spermatophytes, 
but  it  should  be  remembered  that  they  are  simply  other 
names  for  structures  found  in  the  lower  groups. 


Fig.  145.  Finns  Larido,  sliowing  ti])  of  branch  bearing  noedlc-lcaves,  scale-leaves, 
and  cones  (strobili):  a.  very  young  carpellate  cones,  at  time  of  pollination,  borne 
at  tip  of  the  young  shoot  upon  which  new  leaves  are  appearing;  b,  carpellate  cones 
one  year  old;  c,  carpellate  cones  two  years  old,  the  scales  spreading  and  shedding 
the  seeds;  d,  young  shoot  bearing  a  cluster  of  staminate  cones. — Caldwell. 


176 


PLANT  STRUCTURES 


The  strobilus  composed  of  microsporophylls  may  be 
called  the  sfaminate  strobilus — that  is,  one  comjDosed  of 
stamens ;  it  is  often  called  the  staminate  cone,  "  cone " 
being  the  English  translation  of  the  word  "strobilus." 
Frequently  the  staminate  cone  is  spoken  of  as  the  "male 
cone,"  as  it  was  once  supposed  that  the  stamen  is  the 


Fig.  146.  Stamirate  cone  (strobilus)  of  pine  (Pmtis):  A,  section  of  cone,  sliowing 
microsporophylls  (stamens)  bearing  microsporangia;  B,  longitudinal  section  of  a 
single  stamen,  showing  the  large  sporangium  beneath  ;  C,  cross-section  of  a  sta- 
men, showing  the  two  sporangia;  Z>,  a  single  microspore  (pollen  grain)  much  en- 
larged, showing  the  two  wings,  and  a  male  gametophyte  of  two  cells,  the  lower 
and  larger  (wall  cell)  developing  the  pollen  tube,  the  upper  and  smaller  (genera- 
tive cell)  giving  rise  to  the  sperms. — After  Sthasburger. 

male  organ.  This  name  should,  of  course,  be  abandoned, 
as  the  stamen  is  now  known  to  be  a  microsporophyll,  which 
is  an  organ  produced  by  the  sjiorophyte,  which  never  pro- 
duces sex  organs.  It  should  be  borne  distinctly  in  mind 
that  the  stamen  is  not  a  sex  organ,  for  the  literature  of 
botany  is  full  of  this  old  assumption,  and  the  beginner  is  in 


SPERMATOPIIYTKS:   c;YM.\(  JSl'HUMS  ]  77 

danger  of  becoming  confused  and  of  forgetting  that  pollen 
grains  are  asexual  spores. 

98.  Megasporophylls. — The  strobili  composed  of  mega- 
sporophylls  become  much  larger  than  the  others,  forming 


Fio.  147.  Pimts  sylvestrig,  showing  mature  cone  partly  sectioned,  and  showing  car- 
pels (sq,  sq^,  sq^)  with  seeds  in  their  axils  (q),  in  which  the  embryos  (em)  may  be 
distinguished;  A,  a  young  carpel  with  two  megaspcrangia;  B,  an  old  carpel  with 
mature  seeds  (ch),  the  micropyle  being  below  (Jf/").— After  Besset. 


the  well-known  cones  so  characteristic  of  pines  and  their 
allies  (Figs.  US,  a,  b,  c,  163).  Each  sporophyll  is  some- 
what leaf-like,  and  at  its  base  upon  the  upper  side  are  two 
megasporangia  (Fig.  147).  It  is  these  sporangia  which  are 
peculiar  in  each  producing  and  retaining  a  solitary  large 
megaspore.     This  megasporc  rct^embles  a  sac-like  cavity  in 


178 


PLANT   STRUCTURES 


the  body  of  the  sporangium  (Fig.  148,  d),  and  was  at  first 
not  recognized  as  being  a  spore. 

These  structures  had  also  received  names  before  they 
were  identified  with  the  corresponding  structures  of  the 
lower  groups.  The  megasporophyll  was  called  a  carpel, 
the  megasporangia  ovules,  and  the  megaspore  an  embryo- 
sac,  because  the  young  embryo  was  observed  to  develop 
Avithin  it  (Fig.  147,  em). 

The  strobilus  of  megasporophylls,  therefore,  may  be 
called  the  carjjellate  strohilus  or  carpellate  cone.  As  the 
carpel  enters  into  the  organization  of  a  structure  known  as 
the  pistil,  to  be  described  later,  the  cone  is  often  called 
the  pistillate  cone.  As  the  staminate  cone  is  sometimes 
wrongly  called  a  "male  cone,"  so  the  carpellate  cone  is 
wrongly  called  a  ''female  cone,"  the 
old  idea  being  that  the  carpel  with 
its  ovules  represented  the  female  sex 
organ. 

The  structure  of  the  megaspo- 
rangium,  or  ovule,  must  be  known. 
The  main  body  is  the  nucelhis  (Figs. 
148,  c,.  149,  nc)  ;  this  sends  out  from 
near  its  base  an  outer  membrane 
[integwnent)  which  is  distinct  above 
(Figs.  148  i,  149  i),  covering  the  main 
part  of  the  nucellus  and  projecting 
beyond  its  apex  as  a  prominent  neck, 
the  passage  through  which  to  the  apex 
of  the  nucellus  is  called  the  micropyle 
("little  gate")  (Fig.  148,  a).  Cen- 
trally placed  within  the  body  of  the 
nucellus  is  the  conspicuous  cavity 
called  the  embryo-sac  (Fig.  148,  d), 
in  reality  the  retained  megaspore. 
The  relations  between  integument,  micropyle,  nucellus, 
and  embryo-sac  should  be  kept  clearly  in  mind.     In  the 


Fig.  148.  Diagram  of  the 
carpel  structures  of  pine, 
showing  the  heavy  scale 
{A)  which  bears  the 
ovule  (B),  in  which  are 
seen  the  micropyle  (a), 
integument  ib),  nucellus 
(c),  embryo  sac  or  mega- 
spore ((?).— Moore. 


SPERMATOPHYTES :   GYMNOSPEKMS 


179 


nc 


pine  the  micropyle  is  directed  downward,  toward  the  base 
of  the  sporophyll  (Figs.  147,  148). 

99.  Female  gametophyte. — The  female  gametophyte  is 
always  produced  by  the  germination  of  a  megaspore,  and 
therefore  it  should  be 
jjroduced  by  the  so- 
called  embryo-sac  with- 
in the  ovule.  This  im- 
bedded megaspore  ger- 
minates, just  as  does 
the  megaspore  of  Se- 
laginella  or  Isoetes,  by 
cell  division  becoming 
filled  with  a  compact 
mass  of  nutritive  tissue 
representing  the  ordi- 
nary cells  of  the  female 
prothallium  (Fig.  149, 
e).  This  prothallium 
naturally  does  not 
protrude  beyond  the 
boundary  of  the  mega- 
spore wall,  being  com- 
pletely surrounded  by 
the  tissues  of  the 
sporangium.  It  must 
be  evident  that  this 
gametophyte  is  abso- 
lutely dependent  upon 
the  sporophyte  for  its 
nutrition,  and  remains 
not  merely  attached  to 
it,  but  is  actually  im- 
bedded within  its  tis- 
sues like  an  in-ternal  parasite.  So  conspicuous  a  tissue 
within  the  ovule,  as  well  as  in  the  seed  into  which  the 


Fig.  149.  Diagrammatic  section  through  ovule 
(megasporangium)  of  spruce  (Picea).  showing 
integument  (i),  nucellus  (nc),  endosperm  or 
female  gametophyte  (e)  which  fills  the  large 
megaspore  imbedded  in  the  nucellus,  two 
archegonia  (a)  with  short  neck  (c)  and  venter 
containing  the  egg  (o).  and  position  of  ger- 
minating pollen  grains  or  microspores  (p) 
whose  tubes  (/)  penetrate  the  nucellus  tissue 
and  reach  the  archegonia.— After  Schimper. 


XgO  PLANT   STEUCTURES 

ovule  develops,  did  not  escape  early  attention,  and  it  was 
called  e)idosperm,  meaning  "  within  the  seed."  The  endo- 
sperm of  Gymnosperms,  therefore,  is  the  female  gameto- 
phyte. 

At  the  margin  of  the  endosperm  nearest  the  micropyle 
regular  flask-shaped  archegonia  are  developed  (Fig.  149,  a), 
making  it  sure  that  the  endosperm  is  a  female  gameto- 
phyte.  It  is  evident  that  the  necks  of  these  archegonia 
(Fig.  149,  c)  are  shut  away  from  the  approach  of  sperms  by 
swimming,  and  that  some  new  method  of  approach  must  be 
developed. 

100.  Male  gametophyte. — The  microspores  are  developed 
in  the  sporangium  in  the  usual  tetrad  fashion,  and  are  pro- 
duced and  scattered  in  very  great  abundance.  It  will  be 
remembered  that  the  male  gametophyte  developed  by  the 
microspore  of  Selaginella  is  contained  entirely  within  the 
spore,  and  consists  of  a  single  ordinary  prothallial  cell 
and  one  antheridium  (see  §  89).  In  the  pine  it  is  no  bet- 
ter developed.  One  or  two  small  cells  appear,  which  may 
be  regarded  as  representing  prothallial  cells,  while  the  rest 
of  the  gametophyte  seems  to  be  a  single  antheridium  (Fig. 
146,  D).  At  first  this  antheridium  seems  to  consist  of  a 
large  cell  called  the  toall  cell,  and  a  small  one  called  the 
generative  cell.  Sooner  or  later  the  generative  cell  divides 
and  forms  two  small  cells,  one  of  Avhich  divides  again  and 
forms  two  cells  called  male  cells,  which  seem  to  represent 
the  sperm  mother  cells  of  lower  plants.  The  three  active 
cells  of  the  completed  antheridium,  therefore,  are  the  wall 
cell,  with  a  prominent  nucleus,  and  two  small  male  cells 
which  are  free  in  the  large  wall  cell. 

These  sperm  mother  cells  (male  cells)  do  not  form 
sperms  within  them,  as  there  is  no  water  connection  be- 
tween them  and  the  archegonia,  and  a  new  method  of 
transfer  is  provided.  This  is  done  by  the  wall  cell,  which 
develops  a  tube,  known  as  the  pollen-tuhe.  Into  this  tube 
the  male  cells  enter,  and  as  it  penetrates  among  the  cells 


SPEEMATOPHYTES :  GYMNOSPEEMS 


181 


which  shut  off  the  archegonia  it  carries  the   male  cells 
along,  aud  so  they  are  brought  to  the  archegonia  (Fig.  150). 


Fig.  150.  Tip  of  pollen  tube  of  pine, 
showing  the  two  male  cells  (A,  B), 
two  nuclei  ( C)  which  accompany 
them,  and  the  numerous  food 
granules  {D) :  the  tip  of  the  tube 
is  just  about  to  enter  the  neck  of 
the  archegonium.— Caldwell. 


Fig.  151.  Pollen  tube  passing  through  the 
neck  of  an  archegonium  of  spruce  (Picea), 
and  containing  near  its  tip  the  two  male 
nuclei,  wiich  are  to  be  discharged  into  the 
egg  whose  cytoplasm  the  tube  is  just  en- 
tering.—After  Strasbdkger. 


101.  Fertilization. — Before  fertilization  can  take  place 
the  pollen-grains  (microspores)  must  be  brought  as  near  as 
possible  to  the  female  gametophyte  with  its  archegonia. 
The  spores  are  formed  in  very  great  abundance,  are  dry 
and  powdery,  and  are  scattered  far  and  wide  by  the  wind. 
In  the  pines  and  their  allies  the  pollen-grains  are  winged 
(Fig.  146,  />),  so  that  they  are  well  organized  for  wind  dis- 
tribution. This  transfer  of  pollen  is  called  pollination,  and 
those  plants  that  use  the  wind  as  an  agent  of  transfer  are 
said  to  be  anemopliilous,  or  ''wind-loving." 

The  pollen  must  reach  the  ovule,  and  to  insure  this  it 

must  fall  like  rain.     To  aid  in  catching  the  falling  pollen 

the  scale-like  carpels  of  the  cone  spread  apart,  the  pollen 

grains  slide  down  their  sloping  surfaces  and  collect  in  a 

30 


18^ 


PLANT   STKUCTURES 


little  drift  at  the  bottom  of  each  carpel,  where  the  ovules 
are  found  (Fig.  147,  A,  B).  The  flaring  lips  of  the  micro- 
pyle  roll  inward  and  outward  as  they  are  dry  or  moist,  and 
by  this  motion  some  of  the  pollen-grains  are  caught  and 
pressed  down  upon  the  apex  of  the  nucellus. 

In  this  position  the  pollen-tube  develops,  crowds  its 
way  among  the  cells  of  the  nucellus,  reaches  the  wall  of 
the  embryo-sac,  and  penetrating  that,  reaches  the  necks 
of  the  archegonia  (Fig.  149,  jo,  t)  ;  crowding  into  them 
(Fig.  151),  the  tip  of  the  tube  opens,  the  male  cells  are 


/!5^r'fH:?^^^;A^-    sn 


v-^m. 


Fig.  152.  Fertilization  in  spruce  (Picea):  B  is  an  egg,  in  the  tip  of  which  a  pollen 
tube  (p)  has  entered  and  has  discharged  into  the  cytoplasm  a  male  nucleus  (sn). 
which  is  to  unite  with  the  egg  (female)  nucleus  (on);  C,  a  later  stage  in  which  the 
two  nuclei  are  uniting. — After  Schimpbr. 


discharged,  one  male  cell  fuses  with  the  egg  (Fig.  152), 
and  fertilization  is  accomplished,  an  oospore  being  formed 
in  the  venter  of  the  archegonium. 

It  will  be  noticed  that  the  cell  which  acts  as  a  male 
gamete  is  really  the  sperm  mother  cell,  which  does  not 
organize  a  sperm  in  the  absence  of  a  water  connection. 
This  peculiar  method  of  transferring  the  male  cells  by 
means  of  a  special  tube  developed  by  the  antheridium  is 


SPEKMATOPHYTES :  GYMNOSPEKMS 


183 


called  siplionogamy,  which  means  "sexual  reproduction  by 
means  of  a  tube."  So  important  is  this  character  among 
Spermatophytes  that  some  have  proposed  to  call  the  group 
Siphonogams. 

102.  Development  of  the  embryo.— The  oospore  when 
formed  lies  at  the  surface  of  the  endosperm  (female  gameto- 
phyte)  nearest  to  the  micropyle.  As  the  endosperm  is  to 
supply  nourishment  to  the  em- 
bryo, this  position  is  not  the 
most  favorable.  Therefore,  as 
in  Selaginella,  the  oospore  first 
develops  a  suspensor,  which  in 
pine  and  its  allies  becomes  very 
long  and  often  tortuous  (Fig. 
153,  A,  s).  At  the  tip  of  the 
suspensor  the  cell  or  cells  (em- 
bryo cells)  which  are  to  develop 
the  embryo  are  carried  (Fig.  153, 
A,  ka),  and  thus  become  deeply 
buried,  about  centrally  placed, 
in  the  endosperm. 

Several  suspensors  may  start 
from  as  many  archegonia  in  the 
same  ovule,  and  several  embryos 
may  begin  to  develop,  but  as  a 
rule  only  one  survives,  and  the 
solitary  completed  embryo  (Fig. 
153,  B)  lies  centrally  imbedded 

in  the  endosperm  (Fig.  153^/).  The  development  of  more 
than  one  embryo  in  a  megasporangium  (ovule)  is  called 
polyembryony,  a  phenomenon  natural  to  Gymnosperms  with 
their  several  archegonia  upon  a  single  gametophyte. 

103.  The  seed. — While  the  embryo  is  developing  some 
important  changes  are  taking  place  in  the  ovule  outside 
of  the  endosperm.  The  most  noteworthy  is  the  develop- 
ment of  a  special  tissue  that  forms  a  hard  bouy  covering, 


Fig.  153.  Embryos  of  pine:  .1, 
very  young  embryos  (ka)  at  the 
tips  of  long  and  contorted  sus- 
pensors (s)\  B,  older  embryo, 
showing  attachment  to  suspen- 
sor (,«),  the  extensive  root  sheath 
(wh),  root  tip  (u's),  stem  tip 
(r),  and  cotyledons  (c).— After 
Strasburger. 


184 


PLANT   STRUCTURES 


known  as  the  seed  coat,  or  testa  (Fig.  153a).  The  devel- 
opment of  this  testa  hermetically  seals  the  structures  with- 
in, further  development  and  activity 
are  checked,  and  the  living  cells  pass 
into  the  resting  condition.  This  pro- 
tected structure  with  its  dormant  cells 
is  the  seed. 

In  a  certain  sense  the  seed  is  a  transformed  ovule  (mega- 
sporangium),  but  this  is  true  only  as  to  its  outer  configura- 


FiG.  153a.    Pine  seed. 


Fig.  154.    Pine  seedlings,  showing  fee  long  hypocotyl  and  the  nnmerous  cotyledons, 
with  the  old  seed  case  still  attached.— After  Atkinson. 


SPEEMATOPIIYTES:   GYMNOSPERMS  185 

tion.  If  the  internal  structures  be  considered  it  is  much 
more.  It  is  made  uj)  of  structures  belonging  to  three  gen- 
erations, as  follows  :  (1)  The  old  sporophyte  is  represented 
by  seed  coat  and  nucellus,  (2)  the  endosperm  is  a  gameto- 
phyte,  while  (3)  the  embryo  is  a  young  sporophyte.  It  can 
hardly  be  said  that  the  seed  is  simple  in  structure,  or  that 
any  real  conception  of  it  can  be  obtained  without  approach- 
ing it  by  way  of  the  lower  groups. 

The  organization  of  the  seed  checks  the  growth  of  the 
embryo,  and  this  development  within  the  seed  is  known  as 


Fig.  155.    A  cycad,  Rliowiiii;  the  palm-like  habit,  with  much  branched  leaves  and 
scaly  Ptem. — Frimi  '■  Plant  Relations." 

the  infra-seminal  development.  In  this  condition  the  em- 
bryo may  continue  for  a  very  long  time,  and  it  is  a  ques- 
tion whether  it  is  death  or  suspended  animation.  Is  a  seed 
alive  ?  is  not  an  easy  question  to  answer,  for  it  may  be  kept 
in  a  dried-out  condition  for  years,  and  then  when  placed 
in  suitable  conditions  awaken  and  put  forth  a  living  plant. 


5  — 


g  s 


c  -a 


C3 


2  a,-! 
fc  >  <! 
5-  =^  o 


F  .5    ? 


SPERMATOPHYTES:  GYMNOSPERMS 


187 


This  "  awakening  "  of  the  seed  is  spoken  of  as  its  ''  ger- 
mination," but  this  must  not  be  confused  with  the  germi- 
nation of  a  spore,  which  is  real  germination.  In  the  case 
of  the  seed  an  oospore  has  germinated  and  formed  an  embryo, 
which  stops  growing  for  a  time,  and  then  resumes  it.  This 
resumption   of  growth  is   not   germination,  but  is   what 


Fig.  157.    Tip  of  pollen  tube  of  Cycas  reTobiia.  containing  the  two  spiral,  multiciliate 
sperms. — After  Ikeno. 

happens  when  a  seed  is  said  to  "  germinate."  This  second 
period  of  development  is  known  as  the  extra-seminal,  for  it 
is  inaugurated  by  the  escape  of  the  sporophyte  from  the 
seed  (Fig.  154). 

104.    The  great  groups  of  Gynmosperms. — There  are  at 
least  four  living  groups  of  Gymnosperms,  and  two  or  three 


Fig.  158.    A  pine  (Pinus)  showing  the  central  shaft  and  also  the  bunching  of  the 
needle  leaves  toward  the  tips  of  the  branches.— From  "  Plant  Relations." 


SPERMAT0PIIYTE8 :  GYMNOSPERMS 


189 


extinct  ones.     The  groups  differ  so  widely  from  one  an- 
other in  habit  as  to  show  that  Gymnosperms  can  be  very 
much  diversified.    They  are  all  woody  forms,  but  they  may 
be   trailing  or  straggling 
shrubs,  gigantic  trees,  or 
high-climbing  vines ;  and 
their  leaves  may  be  nee- 
dle-like, broad,  or  "fern- 
like."   For  our  purpose  it 
will  be  only  necessary  to 
define  the  two  most  prom- 
inent groups. 

105.  Cycads.  —  Cycads 
are  tropical,  fern  -  like 
forms,  with  large  branched 
(compound)  leaves.  The 
stem  is  either  a  columnar 
shaft  crowned  with  a  ro- 
sette of  great  branching 
leaves,  with  the  general 
habit  of  tree-ferns  and 
palms  (Figs.  155,  156)  ; 
or  they  are  like  great  tu- 
bers, crowned  in  the  same 
way.  In  ancient  times 
(the  Mesozoic)  they  were 
very  abundant,  forming 
a  conspicuous  feature  of 
the  vegetation,  but  now 
they  are  represented  only 
by  about  eighty  forms 
scattered  through  both 
the  oriental  and  occiden- 
tal tropics.  Fig.  159.  The  giant  redwood  {Sequoia  gi- 
Tbpv  fli'P  VPrv  fprn-  ya«<«a)  of  California :  the  relative  eize 
±.11^^  die  veiy  xeiii  is  indicated  by  the  figure  of  a  man  stand- 
like    in    structure    as    well               Ing  at  the  right.— After  Williamson. 


190 


PLANT  STKDCTUKES 


as  in  appearance,  but  they  produce  seeds  and  must  be 
associated  with  Spermatophytes,  and  as  the  seed  is  ex- 
posed they  are  Gymnosperms.     A  discovery  has  been  made 

recently  that  strikingly 
^^7^^jj^  '  ^  """r-zjTj^'s^ij  =^-^  emphasizes  their  f ern- 
^#^:--  i  ---i/"^/^      like  structure.     In  fer- 

tilization a  pollen-tube 
develops,  as  described 
for  pine  and  its  allies, 
but  the  male  cells 
(sperm  mother  -  cells) 
which  it  contains  or- 
ganize sperms,  and 
these  sperms  are  of 
the  coiled  multiciliate 
type  (Fig.  157)  charac- 
teristic of  all  the  Pter- 
idophytes  except  Club- 
mosses.  This  associa- 
tion of  the  old  ciliated 
sperm  habit  with  the 
new  pollen-tube  habit 
is  a  very  interesting  in- 
termediate or  transition 
condition.  It  should  be 
said  that  these  sperms 
have  been  actually  found 
in  but  few  species  of 
the  Cycads,  but  there 
are  reasons  for  suppos- 
ing that  they  may  be 
found  in  all.  Another 
one  of  the  Gymnosperm 

Fig.    160.     An   araucarian   pine   {Araxicana^,  ''  '• 

showing  the  central  shaft,  and  the  regular  grOUpS,  represented   to- 

cycles  of  branches  spreading  in  every  direc-  ^^^    Only    by    the    COm- 
tion  and  bearing  numerous  email  leaves. —  .    .  .,  .  . 

From  "  Plant  Relations."  mouly  Cultivated  maid- 


SPEKMATOPHYTES :  GYMNOSPERMS 


191 


enhair  tree  {Gingko),  with  broad  dichotomously  veined 
leaves,  also  develops  multiciliate  sperms. 

The  testa  of  the  seed,  instead  of  being  entirely  hard  as 
described  for  pine  and  its  allies,  develops  in  two  layers,  the 
inner  hard  and  bony,  and  the  outer  pulpy,  making  the  ripe 
fruit  resemble  a  plum. 

106.  Conifers. — This  is  the  great  modern  Gymnosperm 
group,  and  is  characteristic  of  the  temperate  regions,  where 
it  forms  great  forests.  Some  of  the  forms  are  widely  dis- 
tributed, as  the  great  genus  of  pines  {Finns)  (Fig.  158), 
while  some  are  now  very  much  restricted,  although  for- 
merly very  widely  distributed,  as  the  gigantic  redwoods 
{Sequoia)  of  the  Pacific  slope  (Fig.  159).  The  habit  of 
the  body  is  quite  charac- 
teristic, a  central  shaft 
extending  continuously  to 
the  very  top,  while  the 
lateral  branches  spread 
horizontally,  with  dimin- 
ishing length  to  the  top, 
forming  a  conical  outline 
(Figs.  160,  162).  This 
habit  of  firs,  pines,  etc., 
gives  them  an  appearance 
very  distinct  from  that  of 
other  trees. 

Another  peculiar  fea- 
ture is^  furnished  by  the 
characteristic  ''needle- 
leaves,"  which  seem  to  be 

poorly  adapted  for  foliage.  These  leaves  have  small  spread 
of  surface  and  very  heavy  protecting  walls,  and  show 
adaptation  for  enduring  hard  conditions  (Fig.  161).  As 
they  have  no  regular  period  of  falling,  the  trees  are  always 
clothed  with  them,  and  have  been  called  "  evergreens." 
There  are  some  notable  exceptions  to  this,  however,  as  in 


Fig.  161. — Cross-section  of  a  needle-leaf  of 
pine,  showing  epidermis  (e)  in  which 
there  are  sunken  stomata  (sp),  heavy- 
walled  hypodermal  tissue  (««)  which 
gives  rigidity,  the  mesophyll  region  (p) 
in  which  a  few  resin-ducts  (h)  are  seen, 
and  the  central  region  {stele)  in  which 
two  vascular  bundles  are  developed.— 
After  Sachs. 


KiQ.  162.  A  larch  {Larix),  sTiowing  the  continuous  central  shaft  and  horizontal 
brandies,  the  geneial  outline  being  distinctly  conical.  The  larch  is  peculiar 
among  Conifers  in  periodically  shedding  its  leaves. — From  •'  Plant  Relations." 


SPERMATOPIIYTES :  GYMNOSPERMS 


193 


the  case  of  the  common  larch  or  tamarack,  which  sheds 
its  leaves  every  season  (Fig.  162).  There  are  Conifers, 
also,  which  do  not  produce  needle-leaves,  as  in  the  com- 
mon arbor-vitge,  whose  leaves  consist  of  small  closely-over- 
lapping scale-like  bodies 
(Fig.  163). 

The  two  types  of  leaf 
arrangement  may  also  be 
noted.  In  most  Conifers 
the  leaves  are  arranged 
along  the  stem  in  spiral 
fashion,  no  two  leaves 
being  at  the  same  level. 
This  is  known  as  the  spi- 
ral or  alternate  arrange- 
ment. In  other  forms,  as 
the  cypresses,  the  leaves 
are  in  cycles,  as  was  men- 
tioned in  connection  with 
the  Horsetails,  the  ar- 
rangement being  known 
as  the  cyclic  or  whorhd. 

The  character  which 
gives  name  to  the  group 
is  the  "cone" — that  is, 
the  prominent  carpellate 
cone    which    becomes    so 


Fig.  163.  Arbor-vit;e  (Thvja),  showing  a 
branch  with  6caly  overlapping  leaves, 
and  some  carpellate  cones  (strobili). — 
After  EicHLER. 


conspicuous  m  connec- 
tion with  the  ripening  of 
the  seeds.  These  cones 
generally   ripen    dry   and 

hard  (Figs.  11-5,  147,  163),  but  sometimes,  as  in  junipers, 
they  become  pulpy  (Fig.  161),  the  whole  cone  forming  the 
so-called  "berry." 

There  are  two  great  groups  of   Conifers.     One,  repre- 
sented  by  the  jaines,  has    true   cones  which  conceal  the 


19i: 


PLANT   STKUCTUEES 


ovules,  and  the  seeds  ripen  dry.  The  other,  represented 
by  the  yews,  has  exposed  ovules,  and  the  seed  either  ripens 
fleshy  or  has  a  fleshy  investment. 


FiQ.  164.  The  common  juniper  {Jt/nlperus  communift);  the  branch  to  the  left  bearing 
staminate  strobili;  that  to  the  right  bearing  staminate  strobili  above  and  carpel- 
late  strobili  below,  which  latter  have  matured  into  the  fleshy,  berry-like  fruit. 
—After  Berg  and  Schmidt. 


CHAPTEE  XII 

SPERMATOPHYTES :  ANGIOSPERMS 

107.  Summary  of  Gymnosperms. — Before  beginning  An- 
giosperms  it  is  well  to  state  clearly  the  characters  of  Gym- 
nosperms which  have  set  them  apart  as  a  distinct  group  of 
Spermatophytes,  and  which  serve  to  contrast  them  with 
Angiosperms. 

(1)  The  microspore  (pollen-grain)  by  wind-pollination 
is  brought  into  contact  with  the  megasporangium  (ovule), 
and  there  develops  the  pollen-tube,  which  penetrates  the 
nucellus.  This  contact  between  pollen  and  ovule  implies 
an  exposed  or  naked  ovule  and  hence  seed,  and  therefore 
the  name  "  Gymnosperm." 

(2)  The  female  gametophyte  (endosperm)  is  well  organ- 
ized before  fertilization. 

(3)  The  female  gametophyte  produces  archegonia. 

108.  General  characters  of  Angiosperms. — This  is  the  great- 
est group  of  plants,  both  in  numbers  and  importance,  being 
estimated  to  contain  about  100,000  species,  and  forming 
the  most  conspicuous  part  of  the  vegetation  of  the  earth. 
It  is  essentially  a  modern  group,  replacing  the  Gymnosperms 
which  were  formerly  the  dominant  Seed-plants,  and  in  the 
variety  of  their  display  exceeding  all  other  groups.  The 
name  of  the  group  is  suggested  by  the  fact  that  the  seeds 
are  inclosed  in  a  seed  case,  in  contrast  with  the  exposed 
seeds  of  the  Gymnosperms. 

These  are  also  the  true  flowering  plants,  and  the  ap- 
pearance  of  true   flowers   means  the  development  of  an 

195 


106 


PLANT   STRUCTURES 


elaborate  symbiotic  relation  between  flowers  and  insects, 
through  which  pollination  is  secured.  In  Angiosperms, 
therefore,  the  wind  is  abandoned  as  an  agent  of  pollen 
transfer  and  insects  are  used ;  and  in  passing  from  Gym- 
nosperms  to  Angiosperms  one  passes  from  anemophilous  to 
etitomophilous  ("insect-loving")  plants.  This  does  not 
mean  that  all  Angiosperms  are  entomophilous,  for  some  are 
still  wind-pollinated,  but  that  the  group  is  prevailingly  ento- 
mophilous. This  fact,  more  than  anything  else,  has  re- 
sulted in  a  vast  variety  in  the  structure  of  flowers,  so  char- 
acteristic of  the  group. 

109.  The  plant  body. — This  of  course  is  a  sporophyte, 
the  gametophytes  being  minute  and  concealed,  as  in  Gym- 
nosperms.  The  sporophyte  represents  the  greatest  possible 
variety  in  habit,  size,  and  duration,  from  minute  floating 
forms  to  gigantic  trees ;  herbs,  shrubs,  trees.;  erect,  pros- 
trate, climbing  ;  aquatic,  terrestrial,  epiphytic  ;  from  a  few 
days  to  centuries  in  duration. 

Eoots,  stems,  and  leaves  are  more  elaborate  and  vari- 
ously organized  for  work  than  in  other  groups,  and  the 
whole  structure  represents  the  high- 
est organization  the  plant  body  has 
attained.  .  As  in  the  Gymnosperms, 
the  leaf  is  the  most  variously  used 
organ,  showing  at  least  four  distinct 
modifications  :  (1)  foliage  leaves,  (2) 
scales,  (3)  sporophylls,  and  (4)  floral 
leaves.  The  first  three  are  present 
in  Gymnosperms,  and  even  in  Pteri- 
dophytes,  but  floral  leaves  are  pecul- 
iar to  Angiosperms,  making  the  true 
flower,  and  being  associated  with  en- 
tomophily. 

110.  Microsporophylls. — The  micro- 
sporophyll  of  Angiosperms  is  more 
definitely  known  as  a  "  stamen  "  than 


Fig.  165.  Stamens  of  hen- 
bane (Hyoscyamus)  :  A, 
front  view,  showing  fila- 
ment (/)  and  anther  (jj); 
B,  baclc  view,  showing 
the  connective  (c)  be- 
tween the  pollen-sacs. 
—After  ScHiMPKR. 


SPERMATOPIIYTES :   ANGIOSPERMS 


197 


that  of  Gymnosperms,  and  has  lost  any  semblance  to  a  leaf. 
It  consists  of  a  stalk-like  portion,  the  filament;  and  a 
sporangia  -  bearing  portion,  the   anther  (Figs.   165,  167rt). 


Fig.  166.  Cross-section  of  anther  of  thorn  apple  (Datura),  showing  the  four  imbedded 
sporangia  (a,  p)  containing  microspores;  the  pair  on  each  side  will  merge  and 
dehisce  along  the  depression  between  them  for  the  discharge  of  pollen. — After 
Frank. 

The  filament  may  be  long  or  short,  slender  or  broad,  or 
variously  modified,  or  even  wanting.  The  anther  is  simply 
the  region  of  the  sporophyll  which  bears  sporangia,  and  is 


/  #"" 


Fig.  16~.  Diagrammatic  cross-sections  of  anthers:  A,  younger  stage,  showing  the 
four  imbedded  sporangia,  the  contents  of  two  removed,  but  the  other  two  con- 
taining pollen  mother  cells  (pni)  surrounded  by  the  tapetum  (0;  B,  an  older  stage, 
in  which  the  microspores  (pollen  grains)  are  mature,  and  the  pair  of  sporangia  on 
each  side  are  merging  together  to  form  a  single  pollen-sac  with  longitudinal 
dehiscence. — After  Baillon  and  Luerssen. 

therefore  a  composite  of  sporophyll  and  sporangia  and  is 
often  of  uncertain  limitation.     Such  a  term  is  convenient, 
but  is  not  exact  or  scientific. 
31 


198 


PLANT   STRUCTURES 


If  a  young  anther  be  sectioned  transversely  four  sporan- 
gia will  be  found  imbedded  beneath  the  epidermis,  a  pair 
on  each  side  of  the  axis  (Figs.  166, 167).  When  they  reach 
maturity,  the  paired  sj)orangia  on  each  side  usually  merge  to- 
gether, forming  two  spore-containing  cavities  (Fig.  167,  B). 
These  are  generally  called  ''  pollen-sacs,"  and  each  anther  is 
said  to  consist  of  two  pollen-sacs,  although  each  sac  is  made 
up  of  two  merged  sporangia,  and  is  not  the  equivalent  of  the 
pollen-sac  in  Gymnosperms,  which  is  a  single  sporangium. 


Fio.  1C)7«.  Various  forms  of  stamens:  A.  from  Solanmn.  showing  dehiscence  by 
terminal  pores;  B,  from  Arbutus,  showing  anthers  with  terminal  pores  and 
"horns";  C,  from  Be?-beris;  D.  from  Atherosperma,  showing  dehiscence  by 
uplifted  valves;  E,  from  Aquilegia,  showing  longitudinal  dehiscence;  F,  from 
Pojmvia.  showing  pollen-sacs  near  the  middle  of  the  stamen. — After  Engler 
and  Pranti.. 


SPEEMATOPIIYTES :   ANGIOSPERMS 


199 


Fig.  108.  Cross  -  section  of 
anther  of  a  lily  (Bi/to?nus), 
showing  the  separating  walls 
between  the  members  of  each 
pair  of  sporangia  broken 
down  at  z,  forming  a  con- 
tinuous cavity  (pollen  sac) 
which  opens  by  a  longitudi- 
nal slit.— After  Sachs. 


The  opening  of  the  pollen-sac  to  discharge  its  pollen- 
grains  (microspores)  is  called  dehiscence,  which  means  "a 
splitting  open,"  and  the  methods  of 
dehiscence  are  various  (Fig.  lG7rt). 
By  far  the  most  common  metliod 
is  for  the  wall  of  each  sac  to  split 
lengthwise  (Fig.  1G8),  which  is 
called  longitudinal  deliiscence ;  an- 
other is  for  each  sac  to  open  by  a 
terminal  pore  (Fig.  167«),  in  which 
case  it  may  be  prolonged  above  into 
a  tube. 

111.  Megasporophylls.  —  These 
are  the  so-called  "  carpels  "  of  Seed- 
plr.'.ts,  and  in  Angiosperms  they 
are  organized  in  various  ways,  but 
always  so  as  to  inclose  the  mega- 
sporangia  (ovules).     In  the  simplest 

cases  each  carpel  is  independent  (Fig.  169,  A),  and  is  dif- 
ferentiated into  three  regions:    (1)  a  hollow  bulbous  base, 

which  contains  the 
ovules  and  is  the 
real  seed  case, 
known  as  the 
ovary ;  (2)  sur- 
mounting this  is  a 
slender  more  or  less 
elongated  process, 
the  style;  and  (3) 
usually  at  or  near 
the  apex  of  the  style 
a  special  receptive 
surface  for  the  pol- 
len, the  stigma. 

In    other   cases 
several  carpels  to- 


Fi(i.  109.  Types  of  pistils  :  A.  three  simple  pistils 
(iipocf.rpous),  each  showing  ovary  and  style  tii)ped 
with  stigma  ;  B,  a  compound  i)istil  (syncarpous), 
showing  ovary  (/),  separate  styles  (g).  and  stigmas 
(n)\  C,  a  compound  pistil  (syncarpous).  showing 
ovary  (/).  single  style  ig).  and  stigma  in). — After 
Berg  and  Schmidt. 


200 


PLANT   STKUCTUKES 


gether  form  a  common  ovary,  while  the  styles  may  also 
combine  to  form  one  style  (Fig.  1G9,  C),  or  they  may  remain 
more  or  less  distinct  (Fig.  169,  B).  Such  an  ovary  may 
contain  a  single  chamber,  as  if  the  carpels  had  united  edge 
to  edge  (Fig.  170,  A)  ;  or  it  may  contain  as  many  chambers 
as  there  are  constituent  carpels  (Fig.  170,  B),  as  though 
each  carpel  had  formed  its  own  ovary  before  coalescence. 
In  ordinary  phrase  an  ovary  is  either  "  one-celled "  or 
"  several-celled,"  but  as  the  word  "  cell "  has  a  very  differ- 
ent application,  the  ovary  chamber  had  better  be  called  a 
loculus,  meaning  "a  compartment."     Ovaries, 


Fig.  170.  Diagrammatic  sections  of  ovaries:  A,  cross-section  of  an  ovary  with  one 
loculus  and  three  carpels,  the  three  sets  of  ovules  said  to  be  attached  to  the  wall 
(parietal);  B,  cross-section  of  an  ovary  with  three  loculi  and  three  carpels,  the 
ovules  being  in  the  center  (central) ;  C,  longitudinal  section  of  B,  showing  ovules 
attached  to  free  axis  ("  free  central  "). — After  Schimper. 

therefore,  may  have  one  loculus  or  several  loculi.  Where 
there  are  several  loculi  each  one  usually  represents  a  con- 
stituent carpel  (Fig.  170,  B) ;  where  there  is  one  loculus 
the  ovary  may  comprise  one  carpel  (Fig.  169,  A),  or  several 
(Fig.  170,  A). 

There  is  a  very  convenient  but  not  a  scientific  word, 
which  stands  for  any  organization  of  the  ovary  and  the 
accompanying  parts,  and  that  is  pistil.  A  pistil  may  be 
one  carpel  (Fig.  169,  A),  or  it  may  be  several  carpels  or- 
ganized together  (Fig.  169,  B,  C),  the  former  case  being  a 
simple  pistil,  the  latter  a  compomid  pistil.     In  other  words, 


SPERMATOPIIYTES :   ANGIOSPERMS 


201 


any  organization  of  carpels  which  ap- 
pears as  a  single  organ  with  one  ovary 
is  a  pistil. 

The  ovules  (megasporangia)  are 
developed  within  the  ovary  (Fig.  170) 
either  from  the  carpel  wall,  when  they 
are  foliar,  or  from  the  stem  axis  which 
ends  within  the  ovary,  when  they  are 
cauline  (see  §  89).  They  are  similar 
in  structure  to  those  of  Gymnosperms, 
with  integument  and  micropyle,  nu- 
cellus,  and  embryo -sac  (megaspore), 
except  that  there  are  often  two  integu- 
ments, an  outer  and  an  inner  (Fig, 
171). 

112.  The  male  gametophyte. — When  the  pollen-grain 
(microspore)  germinates  there  is  formed  within  it  the  sim- 
plest known  gametophyte  (Fig.   172).      JS^o  trace  of  the 


Fig.  171.  A  diagrammatic 
section  of  an  ovule  of 
Angiosperms,  showing 
outer  integument  (ai), 
inner  integument  (ii), 
micropyle  (m),  nucellus 
(k),  and  embryo  sac  or 
megaspore  {em). — After 
Sacks. 


Fig.  172.  Germination  of  microspore  (pollen  grain)  in  duckweed  (Lemna):  A,  mature 
spore  with  its  nucleus;  B.  nucleus  of  spore  dividing;  C,  two  nuclei  resulting  from 
the  division;  D,  a  large  and  small  cell  following  the  nuclear  division,  forming  the 
two-celled  male  gametophyte;  E,  division  of  smaller  cell  (generative)  to  form  the 
two  male  cells;  F,  the  two  male  cells  completed  and  lying  near  the  large  tube 
nucleus.— Caldwell. 


202 


PLxVNT   STRUCTURES 


ordinary  nutritive  cells  of  the  gametopliyte  remains,  and 
the  whole  structure  seems  to  represent  a  single  antherid- 
ium.  At  first  it  consists  of  two  cells,  the  large  wall  cell 
and  the  small  free  generative  cell  (Fig.  172,  D).     Later 

the  generative  cell  di- 
vides (Fig.  173,  E), 
either  while  in  the 
pollen  -  grain  or  after 
entrance  into  the  pol- 
len-tube, and  two  male 
cells  (sperm  mother- 
cells)  are  formed  (Fig. 
172,  F),  which  do  not 
organize  sperms,  but 
which  function  direct- 
ly as  gametes. 

When  jiollination 
occurs,  and  the  pollen 
has  been  transferred 
from  the  pollen-sacs 
to  the  stigma,  it  is  de- 
tained by  the  minute 
papillae  of  the  stig- 
matic  surface,  which 
also  excretes  a  sweet- 
ish sticky  fluid.  This 
fluid  is  a  nutrient  so- 
lution for  the  micro- 
spores, which  begin  to 
put  out  their  tubes. 
A  pollen-tube  pene- 
trates throng  h  the 
stigmatic  surface,  en- 
ters among  the  tissues 
of  the  style,  which  is  sometimes  very  long,  slowly  or  rap- 
idly traverses  the  length  of  the  style  supplied  with  food  by 


Fig.  173.  Diagram  of  a  longitudinal  section  through 
a  carpel,  to  illustrate  fertilization  with  all  parts 
in  place  :  s,  stigma ;  g,  style ;  o,  ovary ;  ai,  ii, 
outer  and  inner  integuments;  n,  base  of  rucel- 
lus  ;  /,  funiculus  ;  b,  antipodal  cells  ;  c,  endo- 
sperm nucleus;  k,  egg  and  one  synergid;  ]),  pol- 
len-tube, having  grown  from  stigma  and  passed 
through  the  micropyle  (m)  to  the  egg.— After 

LUERSSEN. 


SPERMATOPIIYTES :  ANGIOSPERMS 


203 


its  cells  but  not  penetrating  them,  enters  the  cavity  of  the 
ovary,  passes  through  the  micropyle  of  an  ovule,  penetrates 
the  tissues  of  the  nucellus  (if  any),  and  finally  reaches  and 
pierces  the  wall  of  the  embryo-sac,  within  which  is  the  egg 
awaiting  fertilization  (Fig.  173). 

This  remarkable  ability  of  the  pollen-tube  to  make  its 
way  through  so  much  tissue,  directly  to  the  microj)yle  of 
an  inclosed  ovule,  can  only  be  explained  by  supposing  that 
it  is  under  the  guidance  of  some  strong  attraction. 

113.  The  female  gametophyte. — The  megaspore  (embryo- 
sac)  occupies  the  same  position  in  the  ovule  as  in  Gymno- 
sperms,  but  its  germination  is  remarkably  modified.  The 
development  of  the  female  gametophyte,  the  act  of  fertil- 


FiG.  174.  Lilium  PhUaddpMcum :  to  the  left  a  young  megasporangium  (ovule), 
showing  integuments  ( C),  nucellus  (A),  and  megaspore  (B)  containing  a  large  nu- 
cleus. To  the  right  a  megaspore  whose  nucleus  is  undergoing  the  first  division 
in  the  formation  of  the  gametophyte.— Caldwell. 


ization,  and  the  development  of  endosperm  are  the  three 
subjects  to  be  considered.  If  fertilization  is  not  accom- 
plished the  endosperm  is  usually  not  developed. 

Development. — The    megaspore    nucleus    divides   (Fig. 
17i),  and  one  nucleus  passes  to  each  end  of  the  embryo- 


204 


PLANT   STRUCTURES 


sac  (Fig.  175,  at  left).  Each  of  tliese  nuclei  divide  (Fig. 
175,  at  right),  and  two  nuclei  appear  at  each  end  of  the 
sac  (Fig.  175,  at  middle).     Each  of  the  four  nuclei  divide 


Fig.  175.  Lilium  Philadelphicum :  to  the  left  is  an  embryo-sac  with  a  ganictophyte 
nucleus  iu  each  end;  to  the  right  these  two  nuclei  ar^  dividing  to  form  the  two 
nuclei  shown  in  each  end  of  the  sac  in  the  middle  figure.— Caldwell. 

(Fig.  176,  at  left),  and  four  nuclei  appear  at  each  end  (Fig. 
176,  at  middle).  When  eight  nuclei  have  appeared,  nuclear 
division  stops.  Then  a  remarkable  phenomenon  occurs. 
One  nucleus  from  each  end,  the  two  being  called  "polar 
nuclei,"  moves  toward  the  center  of  the  sac,  the  two  meet 
and  fuse  (Fig.  176,  at  right,  G),  and  a  single  large  nucleus 
is  the  result. 

The  three  nuclei  at  the  end  of  the  sac  nearest  the  micro- 
pyle  are  organized  into  cells,  each  being  definitely  sur- 
rounded by  cytoplasm,  but  there  is  no  wall  and  the  cells 
remain  naked  but  distinct.  These  three  cells  constitute 
the  egg-apparatus  (Fig.  176,  at  right.  A),  the  central  one, 
which  usually  hangs  lower  in  the  sac  than  the  others,  being 
the  Q,gg,  the  two  others  being  the  synergids,  or  "helpers." 
Here,  therefore,  is  an  Oigg  without  an  archegonium,  a  dis- 
tinguishing feature  of  Angiosperms. 


SPERMATOPIIYTES :  ANGIOSFEEMS 


205 


The  three  nuclei  at  the  other  end  of  the  sac  are  also  or- 
ganized into  cells,  and  usually  have  walls.     These  cells  are 
known  as  antipodal  cells  (Fig.  176,  at  right, 
B).     The  large  nucleus  near  the  center  of  A 


the  sac,  formed  by  the  fusion  of  the  two        / 


Fig.  176.  Lilium  Philadelphicum,  showing  last  stages  of  germination  of  megaspore 
before  fertilization:  the  embryo  sac  to  the  left  contains  the  pair  of  nuclei  in  each 
end  in  a  state  of  division  preparatory  to  the  stage  represented  by  the  middle  figure, 
in  which  there  are  four  nuclei  at  each  end ;  the  figure  to  the  right  sliows  an  embryo- 
sac  containing  a  gametophyte  about  ready  for  fertilization,  with  the  egg  apparatus 
(^4)  composed  of  the  two  synergids  and  egg  (central  and  lower),  the  three  antipo- 
dal cells  (B),  and  the  two  polar  nuclei  fusing  (C)  to  form  the  primary  endosperm 
nucleus.— Caldwell. 


polar  nuclei,  is  known  as  the  primary/  endosperm  nucleus 
or  the  definitive  nucleus. 


206 


PLANT   STRUCTUEES 


Fig.  177.  Fertilization  in  the  cotton  plant, 
a  Dicotyledon,  showing  the  pollen  tube  (P) 
passing  through  the  micropyle  and  con- 
taining a  single  sperm  (male  cell),  and  hav- 
ing entered  the  embryo-snc  is  in  contact 
with  one  of  the  synergids  (S)  on  its  way  to 
the  egg  (^).— After  Duggar. 


Fertilization.  —  The 
pollen-tube,  carrying  the 
two  male  cells,  has  passed 
down  the  style  and  en- 
tered the  micropyle  (Fig. 
173).  It  then  reaches  the 
wall  of  the  embryo -sac, 
pierces  it,  and  is  in  con- 
tact with  the  egg-appa- 
ratus (Fig.  177).  When 
it  comes  near  the  egg.,  the 
tip  of  the  tube  breaks  and 
the  two  male  cells  are  dis- 
charged into  the  embryo- 
sac.  One  male  cell  passes 
to  the  Qgg  and  the  two 
nuclei  fuse,  the  resulting 
cell  being  the  oospore, 
which  develops  the  em- 
bryo. The  other  male 
cell  passes  to  the  endo- 
sperm nucleus  and  fuses 
with  it,  the  cell  resulting 
from  this  triple  fusion  of 
a  male  cell  and  two  polar 
nuclei  developing  the 
endosperm  (Fig.  178). 
These  two  simultaneous 
acts  of  fertilization  are 
spoken  of  as  "  double  fer- 
tilization." 

Endosperm.  —  After 
fertilization,  the  primary 
endosperm  nucleus  begins 
a  series  of  divisions,  and 
as  a  result  the  sac  becomes 


SPERM  ATOniYTES :    ANGIOSPEKMS 


207 


more  or  less  filled  with  nutritive 
cells,  which  are  often  organized 
into  a  compact  tissue  (Fig.  179). 
These  nutritive  cells  do  not  cor- 
respond to  the  endosperm  of 
Gymnosjjerms,  although  they  re- 
receive  the  same  name.  In  Gym- 
nosperms  the  endosperm  is  main- 
ly formed  before  fertilization  and 
is  the  nutritive  body  of  the  female 
gametophyte ;  while  in  Angio- 
sperms  it  is  formed  after  fertiliza- 
tion and  is  probably  not  a  part 
of  the  gametophyte.  As  the 
endosperm  of  Angiosperms  is  a 
product  of  what  appears  to  be 
fertilization,  it  would  seem 
proper  to  regard  it  as  sporo- 
phyte  tissue,  but  its  real  character 
The  antipodal  cells  probably 
of  the  gametophyte.  Sometimes 
after  they  are  formed ;  but  some 


•■'">%'-•., 


Fio.  178.  End  of  embryo-sac  of 
Silphium,  showing  double  fer- 
tilization :  sy,  synergid,  the 
other  having  been  destroyed  by 
the  pollen-tube ;  o,  egg  with 
coiled  male  cell  (spi)  lying 
against  its  nucleus ;  e,  endo- 
sperm cell,  with  large  coiled 
male  cell  dyjj)  'yi"n  against  it. 
— After  Land. 


is  still  under  discussion, 
represent  nutritive  cells 
they  disappear  very  soon 
times  they  become  very 


Fig.  179.    One  end  of  the  embryo-sac  in  wake-robin  {Tnllimn),  showing  endosperm 
(shaded  cells)  in  which  a  young  embryo  is  imbedded. — After  Atkinson. 


208 


PLANT   STEDCTUKES 


active  and  even  divide  and  form  a  considerable  amount  of 
tissue,  which  usually  nourishes  the  embryo  until  endosperm 
tissue  is  developed,  and  then  becomes  disorganized ;  or 
even  invades  the  tissue  of  the  nucellus. 

114.  Development  of  embryo. — While  the  endosperm  is 
forming,  the  oospore  has  germinated  and  the  sporophyte 
embryo  is  developing  (Fig.  180).  Usually  a  suspensor,  more 
or  less  distinct,  but  never  so  prominent  as  in  Gymnosperms, 

is  formed ;  at  the  end  of  it  the 
embryo  is  developed  (Fig.  181), 
which,  when  completed,  is  more 
or  less  surrounded  by  nourish- 
ing endosperm  (Fig.  183). 

The  two  groups  of  Angio- 
sperms  differ  widely  in  the  struc- 
ture of  the  embryo.  In  Mono- 
cotyledons the  axis  of  the  em- 
bryo develops  the  root-tip  at  one 
end  and  the  "  seed-leaf  "  (coty- 
ledon) at  the  other,  the  stem-tip 
arising  from  the  side  of  the  axis 
as  a  lateral  member  (Fig.  182). 
This  relation  of  organs  recalls 
the  embryo  of  Isoetes  (see  §  90). 
Naturally  there  can  be  but  one 
cotyledon  under  such  circum- 
stances, and  the  group  has  been 
named  Monocotyledons. 

In  Dicotyledons  the  axis  of 
the  embryo  develops  the  root-tip  at  one  end  and  the  stem- 
tip  at  the  other,  the  cotyledons  (usually  two)  appearing  as 
a  pair  of  opposite  lateral  members  on  either  side  of  the 
stem-tip  (Fig.  181).  This  recalls  the  relation  of  parts  in 
the  embryo  of  Sekiginella  (see  §  89).  As  the  cotyledons 
are  lateral  members  their  number  may  vary.  In  Gymno- 
sperms, whose  embryos  are  of  this  typej  there  are  often 


Fig.  180.  Curved  embryo-sac  of 
arrowhead  (Sagittar'ia),  show- 
ing in  the  upper  right  end  a 
young  embryo,  in  the  other 
end  the  antipodal  cells  cut  off 
by  a  partition,  and  scattered 
through  the  sac  a  few  free  en- 
dosperm cells. — After  Scuaff- 

NER. 


SPEKMATOPIIYTES  .    ANGIOSPERMS 


200 


several  cotyledons  in  a  cycle  (Fig.  154) ;  and  in  Dicotyle- 
dons there  may  be  one  or  several  cotyledons ;  but  as  a  pair 
of  opposite  cotyledons  is  almost  without  exception  in  the 
group,  it  is  named  Dicotyledons. 

The  axis  of  the  embryo  between  the  root-tip  and  the 
cotyledons  is  called  the  hypocotyl  (Figs.  154, 193, 194),  which 


Fig.  181.  Development  of  embryo  of  shepherd's  purse  {Capsella),  a  Dicotyledon: 
beginning  with  /,  the  youngest  stage,  and  following  the  sequence  to  VI,  the  old- 
est stage,  V  represents  the  suspensor,  c  the  cotyledons,  s  the  stem-tip,  w  the  root, 
h  the  root-cap.  Note  the  root-tip  at  one  end  of  the  axis  and  the  stem-tip  at  the 
other  between  the  cotyledons. — After  Hanstein. 


means  "  under  the  cotyledon,"  a  region  which  shows  pecul- 
iar activity  in  connection  with  the  escape  of  the  embryo 
from  the  seed.  Formerly  it  was  called  either  caulicle  or 
radicle.     In  Dicotyledons  the  stem-tip  between  the  coty- 


210 


PLANT   STRUCTURES 


ledons  often  organizes  the  rudiments  of  subsequent  leaves, 
forming  a  little  bud  which  is  called  the  plmnule. 

Embryos  differ  much  as  to  com- 
pleteness of  their  development  within 
the  seed.  In  some  plants,  especially 
those  which  are  parasitic  or  sapro- 
phytic, the  embryo  is  merely  a  small 
mass  of  cells,  without  any  organiza- 
tion of  root,  stem,  or  leaf.  In  many 
cases  the  embryo  becomes  highly  de- 
veloped, the  endosperm  being  used 
up  and  the  cotyledons  stuffed  with 
food  material,  the  plumule  contain- 
ing several  well  -  organized  young 
leaves,  and  the  embryo  completely 
filling  the  seed  cavity.  The  com- 
mon bean  is  a  good  illustration  of 
this  last  case,  the  whole  seed  within 
the  integument  consisting  of  the  two 
large,  fleshy  cotyledons,  between 
which  lie  the  hypocotyl  and  a  plu- 
mule of  several  leaves. 

115.  The  seed.  —  As  in  Gymno- 
sperms,  while  the  processes  above 
described  are  taking  place  within 
the  ovule,  the  tissue  is  developing 
that  forms  the  hard  seed-coat  or  testa  (Fig.  183).  When 
this  hard  coat  is  fully  developed,  the  activities  within 
cease,  and  the  whole  structure  passes  into  that  condition  of 
suspended  animation  which  is  so  little  understood,  and 
which  may  continue  for  a  long  time. 

The  testa  is  variously  developed  in  seeds,  sometimes 
being  smooth  and  glistening,  sometimes  pitted,  sometimes 
rough  with  warts  or  ridges.  Sometimes  prominent  append- 
ages are  produced  which  assist  in  seed-dispersal,  as  the 
wings  in  Catcilim  or  Bignonia  (Fig.  184),  or  the  tufts  of 


Fig.  182.  Yoang  embryo  of 
water  plantain  (Alisma),  a 
Monocotyledon,  the  root 
being  organized  at  one 
end  (next  the  snspensor), 
the  single  cotyledon  (C) 
at  the  other,  and  the  stem- 
tip  arising  from  a  lateral 
notch  (»).  —  After  Han- 
stein. 


SPERMATOPHYTES :   ANGIOSPERMS 


211 


Fig.  183.  The  two  figures  to  the  left  are  seeds  of  violet,  one  showing  the  black,  hard 
testa,  the  other  being  sectioned  and  showing  testa,  endosperm,  and  imbedded 
embryo;  the  figure  to  the  right  is  a  section  of  a  pepper  fruit  (Piper),  showing 
modified  ovary  wall  (pc\.  seed  testa  (sc),  nucellus  tissue  (jj),  endosperm  {en),  and 
embryo  («m). — After  Baillon. 

hair  on  the  seeds  of  milkweed,  cotton,  or  fireweed  (Fig. 
185).  For  a  fuller  account  of  the  methods  of  seed-dispersal 
see  Plant  Relations,  Chapter  VI. 


Fig.  184.    A  winged  seed  of  Bignonia.— After  Strasburger. 

116.  The  fruit— The  effect  of  fertilization  is  felt  beyond 
the  boundaries  of  the  ovule,  which  forms  the  seed.  The 
ovary  is  also  involved,  and  becomes  more  or  less  modiiied. 
It  enlarges  more  or  less,  sometimes  becoming  remarkal)ly 
enlarged.  It  also  changes  in  structure,  often  becoming 
hard  or  parchment-like.  In  case  it  contains  several  or 
numerous  seeds,  it  is  organized  to  open  in  some  way  and 
discharge  them,  as  in  the  ordinary  jjods  and  capstiles  (Fig. 
185).     In  case  there  is  but  one  seed,  the  modified  ovary 


212 


PLANT   STKUCTUKES 


wall  may  invest  it  as  closely  as  another 
integument,  and  a  seed-like  fruit  is 
the  result — a  fruit  which  never  opeus 
and  is  practically  a  seed.  Such  a 
fruit  is  known  as  an  ahene,  and  is 
very  characteristic  of  the  greatest 
Angiosperm  family,  the  Compositas, 
to  which  sunflowers,  asters,  golden- 
rods,  daisies,  thistles,  dandelions, 
etc.,  belong.  Dry  fruits  which  do 
not  open  to  discharge  the  seed  often 
bear  appendages  to  aid  in  dispersal 
by  wind  (Figs.  186, 187),  or  by  animals 
(Fig.  188). 

Capsules,  pods,  and  akenes  are  said 
to  be  dry  fruits,  but  in  many  cases 
fruits   ripen   fleshy.     In   the   peach, 
plum,  cherry,  and  all  ordinary  ''  stone 
fruits,"  the  modified  ovary  wall  or- 
ganizes two  layers,  the  inner  being 
very  hard,  forming  the  "  stone,"  the 
outer  being  pulpy  (Fig.  189),  or  vari- 
ously  modified    (Fig.   190).      In  the   true  berries,   as  the 
grape,   currant,   tomato,  etc.,  the  whole  ovary  becomes  a 
thin-skinned  pulpy  mass  in  which  the  seeds  are  imbedded. 

In  some  cases 
the  effect  of  ferti- 
lization in  chang- 
ing structure  is 
felt  beyond  the 
ovary.    In  the  ap-   W/jj '','.'(: 


pie,  pear,  quince, 
and  sucR  fruits, 
the  pulpy  part  is 
the    modified 

calyx  (one    of  the  Fiq.  ISe.    winged  fruit  of  maple.— After  Kerner. 


Fig.  185.  A  pod  of  fireweed 
{EjAlobi'im)  opening  and 
exposing  its  plumed  seeds 
which  are  transported  by 
the  wind.— After  Beal. 


SPEEMATOPHYTES :  ANGIOSPERMS 


213 


floral  leayes),  tlie  ovary  and  its  contained  seeds  being  repre- 
sented by  the  '^core."  In  other  cases,  the  end  of  the  stem 
bearing  the  ovaries  (receptacle)  becomes  enlarged  and 
pulpy,  as  in  the  strawberry  (Fig.  191).  This  effect  some- 
times involves  even 

more  than  the  ...^-^i/MMm^*.,^ 

parts   of   a    single 
flower,     a     whole     . 
fl  o  w  e  r  -  c  1  u  s  t  e  r,    ^ 
with   its   axis   ami 
bracts,      becoming    ,; 
an  enlarged  pulpy 
mass,    as    in    the 
pineapple   (Fig.  -  \->- 

192).  ■    ' 

The        term 
"fruit,"  therefore, 


Fig.  187.  A  ripe  dandelion  head,  showing  the  mass  of 
plumes,  a  few  seed-like  fruits  (akenes)  with  their 
plumes  still  attached  to  the  receptacle,  and  two 
fallen  off. — After  Kernek. 


Fig.  188.  An  akene  of  beg- 
gar ticks,  showing  the  two 
barbed  appendages  which 
lay  hold  of  animals. — Af- 
ter Beal. 

32 


Fig.  189.  To  the  left  a  section  of  a  peach  (fruit), 
showing  pulp  and  stone  formed  from  ovary  wall, 
and  the  contained  seed  (kernels ;  to  the  right 
the  fruit  of  almond,  which  ripens  dry.— After 
Gray. 


2U 


PLANT   STRUCT UKES 


is  a  very  indefinite  one,  so  far  as  the  structures  it  includes 
are  concerned.  It  is  simply  an  effect  which  follows  fer- 
tilization, and  involves  more  or  less  of  the  structures  adja- 


FiG.  190.  Fruit  of  nutmeg  (Myristica) :  A,  section  of  fruit,  sliovving  seed  within  the 
heavy  wall ;  B.  section  of  seed,  showing  peculiar  convoluted  and  hard  endosperm 
{m)  in  which  an  embryo  (;;)  is  imbedded. — After  Berg  and  Schmidt. 


cent  to  the  seeds, 
only  to  the  ovary 


Fig.  191.  Fruit  of  straw- 
berry, showing  the  per- 
sistent calyx,  and  the  en- 
larged pulpy  receptacle 
in  which  numerous  sim- 
ple and  dry  fruits  (a- 
kenesi  are  imbedded. — 
After  Bailet. 

lodgment.     If  the 
devices  for  burial, 


As  has  been  seen,  this  effect  may  extend 
wall,  or  it  may  include  the  calyx,  or  it 
may  be  specially  directed  toward  the 
receptacle,  or  it  may  embrace  a  whole 
flower-cluster.  It  is  what  is  called  a 
physiological  effect  rather  than  a  defi- 
nite morphological  structure. 

117.  Germination  of  the  seed. — It 
has  been  pointed  out  (§  103)  that  the 
so-called  "  germination  of  the  seed " 
is  not  true  germination  like  that  of 
spores.  It  is  the  awakening  and  es- 
cape of  the  young  sporophyte,  which 
has  long  before  passed  through  its 
germination  stage. 

By  various  devices  seeds  are  separ 
rated  from  the  parent  plant,  are  dis- 
persed more  or  less  widely,  and  find 
lodgment  is  suitable,  there  are  many 
such  as  twisting  stalks  and  awns,  bur- 


SPERMATOPHYTES:   ANGIOSPERMS 


215 


rowing  animals,  etc.  The  period  of  rest  may  be  long  or 
short,  but  sooner  or  later,  under  the  influence  of  moisture, 
suitable  temperature,  and  oxygen  the  quiescent  seed  begins 
to  show  signs  of  life. 

The  sporophyte  within  begins  to  grow,  and  the  seed 
coat  is  broken  or  penetrated  through  some  thin  spot  or 


Pig.  102.  Pineapple:  .-1.  the  cluster  of  fruits  forming  the  so-called  "fruit";  i?,  single 
flower,  showing  small  calyx  and  more  prominent  corolla;  C,  section  of  flower, 
showing  the  floral  organs  arising  above  the  ovary  (ei)igynous). — .4,  B  after  Koch; 
P  after  Lb  Maout  and  Decaisne. 


opening.  The  root-tip  emerges  first,  is  protruded  still 
farther  by  the  rapid  elongation  of  the  hypocotyl,  soon 
curves  toward  the  earth,  penetrates  the  soil,  and  sending 
out  rootlets,  becomes  anchored.     After  anchorage  in  the 


21C 


PLANT   STRUCTURES 


soil,  the  hypocotyl  again  rapidly  elongates  and  develops  a 
strong  arch,  one  of  whose  limbs  is  anchored,  and  the  other 
is  pulling  npon  the  cotyledons  (Fig.  193).  This  pull  finally 
frees  the  cotyledons,  the  hypocotyl  straightens,  the  cotyle- 


FiG.  193.  Germination  of  the  garden  bean,  showing  the  arch  of  the  hypocotyl  above 
ground,  its  pnll  on  the  seed  to  extricate  the  cotyledons  and  plumule,  and  the  final 
straightening  of  the  stem  and  expansion  of  the  young  leaves.— After  Atkinson. 

dons  are  spread  out  to  the  air  and  light,  and  the  young 
sporophyte  has  become  independent  (Fig.  194). 

In  the  grain  of  corn  and  other  cereals,  so  often  used  in 
the  laboratory  as  typical  Monocotyledons,  but  really  excep- 
tional ones,  the  embryo  escapes  easily,  as  it  is  placed  on 
one  side  of  the  seed  near  the  surface.  The  hypocotyl  and 
stem  split  the  thin  covering,  and  the  much-modified  cotyle- 
don is  left  within  the  grain  to  absorb  nourishment. 

In  some  cases  the  cotyledons  do  not  escape  from  the 
seed,  either  being  distorted  with  food  storage  (oak,  buck- 
eye, etc.),  or  being  retained  to  absorb  nourishment  from 
the  endosperm  (palms,  grasses,  etc.).  In  such  cases  the 
stem-tip  is  liberated  by  the  elongation  of  the  petioles  of  the 


SPEEMATOl'IIYTES :    ANGIOSPEEMS 


217 


cotyledons,  and  the  seed  coat  containing  the  cotyledons 
remains  like  a  lateral  appendage  upon  the  straightened  axis. 

It  is  also  to  be  observed  in 
many  cases  that  the  young  root 
system,  after  gripping  the  soil, 
contracts,  drawing  the  young 
plant  deeper  into  the  ground. 

118.  Summary  from  Angio- 
sperms. — At  the  beginning  of  this 
chapter  (§  107)  the  characters  of 
the  Gymnosperms  were  summar- 
ized which  distinguished  them 
from  Angiosperms,  whose  con- 
trasting characters  may  be  stated 
as  follows  : 

(1)  The  microspore  (pollen- 
grain),  chiefly  by  insect  pollina- 
tion, is  brought  into  contact  with 
the  stigma,  which  is  a  receptive 
region  on  the  surface  of  the  car- 
pel, and  there  develops  the  pollen- 
tube,  which  penetrates  the  style 
to  reach  the  ovary  cavity  which 
contains  the  ovules  (megasporan- 
gia).  The  impossibility  of  con- 
tact betAveen  pollen  and  ovule  im- 
plies inclosed  ovules  and  hence 
seeds,  and  therefore  the  name 
"  Angiosperm." 

(2)  The  female  gametophyte 
at  the  time  of  fertilization  con- 
sists of  only  a  few  free  nuclei  and 
cells,  usually  seven  in  number. 

(3)  The  female  gametophyte  produces  no  archegonia, 
but  a  single  naked  egg. 


Fig.  194.  Seedling  of  hornbeam 
( CcD'pinus),  showing  primary 
root  i^hiv)  bearing  rootlets  (sw) 
upon  which  are  numerous 
root  hairs  (;■),  hypocotyl  (h), 
cotyledons  (c),  young  stem 
(«),  and  first  {1}  and  second 
W)  true  leaves.— After  Sciitm- 

PER. 


CHAPTER    XIII 

THE  FLOWER 

119.  General  characters. — In  general  the  flower  may  be 
regarded  as  a  modified  branch  of  the  sporophyte  stem  bear- 
ing sporophylls  and  usually  floral  leaves.  Its  representa- 
tive among  the  Pteridophytes  and  Gymnosperms  is  the  stro- 
bilus,  which  has  sporophylls  but  not  floral  leaves.  Among 
Angiosperms  it  begins  in  a  simple  and  somewhat  indefinite 
way,  gradually  becomes  more  complex  and  modified,  until 
it  appears  as  an  elaborate  structure  very  eflicient  for  its 
purpose. 

This  evolution  of  the  flower  has  proceeded  along  many 
lines,  and  has  resulted  in  endless  diversity  of  structure. 
These  diversities  are  largely  used  in  the  classification  of 
Angiosperms,  as  it  is  supposed  that  near  relatives  are  indi- 
cated by  similar  floral  structures,  as  well  as  by  other  fea- 
tures. The  signiflcance  of  these  diversities  is  supposed  to 
be  connected  with  securing  proper  pollination,  chiefly  by 
insects,  and  favorable  seed  distribution. 

Although  the  evolution  of  flowers  has  proceeded  along 
several  lines  simultaneously,  now  one  feature  and  now 
another  being  emphasized,  it  will  be  clearer  to  trace  some 
of  the  important  lines  separately. 

120.  Floral  leaves. — In  the  simplest  flowers  floral  leaves 
do  not  appear,  and  the  flower  is  represented  only  by  the 
sporophylls.  Both  kinds  of  sporophylls  may  be  associated, 
in  which  case  the  flower  is  said  to  be  'perfect  (Fig.  195) ;  or 
they  may  not  both  occur  in  the  same  flower,  in  which  case 
one  flower  is  stmninate  and  the  other  jnstillate  (Fig.  196). 

218 


THE   FLOWER 


219 


When  the  floral  leaves  first  ajjpear  in  connection  with 
the  sporophylls  they  are  inconspicuous,  scale-like  bodies. 
In  higher  forms  they  become  more  prominent  and  inclose 


Fig.  195.   Lizard's  tail  (Sawr^/rMs):  A,  tip  of  branch 
bearing  leaves  and  elongated  cluster  of  flowers; 

B,  a  single  naked  flower  from  A.  showing  sta- 
mens and  four  spreading  and  stigmatic  styles; 

C,  flower  from  another  species,  showing  sub- 
tending bract,  absence  of  floral  leaves,  seven 
stamens,  and  a  syncarpous  i)istil  ;  the  flowers 
naked  and  perfect. -^Aftcr  Engler. 


Fig.  196.  Naked  flowers  of  dif- 
ferent willows  (Salix),  each 
from  the  axil  of  a  bract : 
a,  b,  c,  staminate  flowers ; 
d,  *>  fy  pistillate  flowers,  the 
pistil  composed  of  two  car- 
pels (syncarpous).  —  After 
Wauming. 


Fig.  197.  Flower  of  calamus 
(Acorvs).  showing  simple 
perianth,  stamens,  and  syn- 
carpous pistil:  a  hypogynous 
flower  without  difl'erentiation 
of  calyx  and  corolla. — After 
Engler. 


Fig.  199.  Common  flax  (Linvm) : 
A.  entire  flower,  showing  calyx 
and  corolla  ;  B,  floral  leaves  re- 
moved, showing  stamens  and 
syi.carpous  pistil  ;  C,  a  mature 
Fig.  198.    Flowers  of  elm  (Z7&»?m)  :  yl,  branch  capsule   splitting   open. —After 

bearing  clusters  of  flowers  and  scaly  buds  ;  Schimper. 

B,  single  flower,  showing  simple  perianth 
and  stamens,  being  a  stamii  ate  flower  ;   C, 

flower  showing  perianth,  stamens,  and  the  two  divergent  styles  stigmatic  on  inner 
surface,  being  a  perfect  flower;  D.  section  through  perfect  flower,  showing  peri- 
anth, stamens,  and  pistil  with  two  loculi  each  with  a  single  ovule — After  Englbr. 


Fig.  200.  A  flower  of  peony,  showing  the  four  sets  of  floral  organs:  Jc,  the  sepals,  to- 
gether called  the  calyx;  c,  the  petals,  together  called  the  corolla;  a,  the  numerous 
stamens;  g,  the  two  carpels,  which  contain  the  ovules. — After  Strasburger. 


THE  FLOWER 


221 


the  young  sporophylls,  but  they  are  all  alike,  forming  what 
is  called  the  perianth  (Figs.  197, 198). 

In  still  higher  forms  the  perianth  differentiates,  the 
inner  floral  leaves  become  more  delicate  in  texture,  larger 
and  generally  brightly  colored  (Fig.  199,  A).  The  outer 
set  may  remain  scale-like,  or  become  like  small  foliage 
leaves.  When  the  dif- 
ferentiation of  the  peri- 
anth is  distinct,  the 
outer  set  of  floral  leaves 
is  called  the  calyx,  each 
leaf  being  a  sejjcd;  the 
inner  set  is  the  corolla, 
each  leaf  being  a  petal 
(Fig.  200).  Sometimes, 
as  in  the  lily,  all  the 
floral  leaves  become 
uniformly  large  and 
brightly  colored,  in 
which  case  the  term 
perianth  is  retained 
(Fig.  201).  In  other 
cases,  the  calyx  may  be 
the  large  and  colored 
set,  but  whenever  there 
is  a  clear  distinction 
between  sets,  the  outer 
is  the  calyx,  the  inner 
the  corolla. 

Both  floral  sets  may 
not  appear,  and  it  has 
become  the  custom  to 

°                                      o  Fig.  201.— An    caster -lily,   a  Monocotyledon, 

as      the      corolla,      such  showing  perianth  (a),  stamens  (6),  stigma  (O, 

flowers       beinc       called  flower  bud  (d),  and  a  carpel  after  the  peri- 

^             ,  anth  has  fallen  (I),  with  its  knob-like  stigma, 

ap  etaloUS,    meaning  long  style,  and  slender  ovary.— Caldwell. 


222 


PLANT   STKUCTDRES 


"  without  petals."  It  is  not  always  possible  to  tell  whether 
a  flower  is  apetalous — that  is,  whether  it  has  lost  a  floral 
set  which  it  once  had — or  is  simply  one  whose  perianth  has 
not  yet  diflierentiatecl,  in  which  case  it  would  be  a  "primi- 
tive type." 

The  line  of  evolution,  therefore,  extends  from  floweVs 
without  floral  leaves,  or  naked  flowers,  to  those  with  a  dis- 
tinctly differentiated  calyx  and  corolla. 

121.  Spiral  to  cyclic  flowers. — In  the  simplest  flowers  the 
sporophylls  and  floral  leaves  (if  any)  are  distributed  about 
an  elongated  axis  in  a  spiral,  like  a  succession  of  leaves. 
That  part  of  the  axis  which  bears  the  floral  organs  is  for 
convenience  called  the  receptacle  (Fig.  202).     As  the  recep- 


FiG.  202.  A  buttercup  (Faminculus):  a,  complete  flower,  showing  sepals,  petals,  sta- 
mens, and  head  of  numerous  carpels  on  a  large  receptacle;  b,  section  showing 
relation  of  parts;  a  hypogynous,  polypetalous,  apocarpous,  actinomorphic  flower. 
—After  Baiilon. 


tacle  is  elongated  and  capable  of  continued  growth,  an  in- 
definite number  of  each  floral  organ  may  appear,  especially 
of  the  sporophylls.  With  the  spiral  arrangement,  there- 
fore, there  is  no  definiteness  in  the  number  of  floral  organs  ; 
there  may  be  one  or  very  many  floral  leaves,  or  stamens,  or 
carpels.  The  spiral  arrangement  and  indefinite  numbers 
are  features  of  the  ordinary  strobilus,  and  therefore  such 
flowers  are  regarded  as  more  primitive  than  the  others. 

In  higher  forms   the   receptacle  becomes  shorter,  the 
spiral  more  closely  coiled,  until  finally  the  sets  of  organs 


THE   FLOWER  223 

appear  to  be  thrown  into  rosettes  or  cycles.  This  change 
does  not  necessarily  affect  all  the  parts  simultaneously. 
For  example,  in  the  common  buttercup  the  sepals  and 
petals  are  nearly  in  cycles,  while  the  carpels  are  spirally 
arranged  and  indefinitely  numerous  on  the  head-like  recep- 
tacle (Fig.  203).     On  the  other  hand,  in  the  common  water- 


FiG.  203.     Flower  of  water-lily  (Nymph<ta),  showing  numerous  petals  and  stamens. — 
After  Caspart. 

lily  the  petals  and  stamens  are  spiral,  and  indefinitely  re- 
peated, while  the  sepals  and  carpels  are  approximately 
cyclic  (Fig.  203). 

Finally,  in  the  highest  forms,  all  the  floral  organs  are 
in  definite  cycles,  and  there  is  no  indefinite  repetition  of 
any  part.  All  through  this  evolution  from  the  spiral  to  the 
cyclic  arrangement  there  is  constantly  apj^earing  a  tend- 
ency to  "  settle  down  "  to  certain  definite  numbers.  When 
the  complete  cyclic  arrangement  is  finally  established  these 
numbers  are  established,  and  they  are  characteristic  of 
great  groups.  In  cyclic  Monocotyledons  there  are  nearly 
always  just  three  organs  in  each  cycle,  forming  what  is 
called  a  trimerous  flower  (Fig.  204) ;  while  in  cyclic  Dicot- 


224: 


PLANT   STKUCTURES 


yledons  the  number  five  prevails,  but  often  four  appears, 
forming  pentwrnerous  or  tetramerous  flowers  (Fig.  199). 
This  does  not  mean  that  there  are  necessarily  just  three, 
four,  or  five  of  each  organ  in  the  flower,  for  there  may  be 
two  or  more  cycles  of  some  one  organ.  For  example,  in  the 
common  lily  there  are  six  floral  leaves  in  two  sets,  six  sta- 
mens in  two  sets,  and  three  carpels  (Fig.  204). 

In  the  cyclic  flowers  it  is  also  to  be  noted  that  each  set 
alternates  with  the  next  set  outside  (Fig.  204).     The  petals 

are  not  directly  opposite  the  se- 
pals, but  are  opposite  the  spaces 
between   sepals ;   the  stamens  in 
^^sX?"""***^  N  turn  alternate  with  the  petals  ;  if 

f  c9/^\'u)^V  there  is  a  second  set  of  stamens, 

'/v,  ^^  f^'l  it  alternates   with  the  outer  set, 

and  so  on.  If  two  adjacent  sets 
are  found  opposing  one  another, 
it  is  usually  due  to  the  fact  that 
a  set  between  has  disappeared. 
For  example,  if  a  set  of  stamens 
is  opposite  the  set  of  petals,  either 
an  outer  stamen  set  or  an  inner 
petal  set  has  disappeared. 

This  line  of  evolution,  there- 
fore, extends  from  flowers  whose 
parts  are  spirally  arranged  upon 
an   elongated  receptacle  and  in- 
definite in  number,  to  those  whose  parts  are  in  cycles  and 
definite  in  number. 

122.  Hypogynous  to  epigynous  flowers. — In  the  simpler 
flowers  the  sepals,  petals,  and  stamens  arise  from  beneath 
the  ovary  (Figs.  197,  202,  205,  1).  As  in  such  cases  the 
ovary  or  ovaries  may  be  seen  distinctly  above  the  origin 
{insertion)  of  the  other  parts,  such  a  flower  is  often  said  to 
have  a  '^  superior  ovary."  The  more  usual  term,  however, 
is  liypogynous,  meaning  in  effect  *'  under  the  ovary,"  refer- 


FiG.  204.  Diagram  of  sucli  a 
flower  as  the  lily,  showing  re- 
lation of  parts  :  uppermost 
organ  is  the  bract  in  the  axil 
of  which  the  flower  occurs ; 
black  clot  below  indicates  po- 
sition of  stem  ;  floral  parts  in 
threes  and  in  five  alternating 
cycles  (two  stamen  sets>,  being 
a  trimerous,  pentacyclic  flow- 
er.— After  ScHiMPER. 


THE   FLOWER 


225 


ring  to  the  fact  that  the  insertion  of  the  other  parts  is 
under  the  ovary. 

Hypogyny  is  rerj  largely  displayed  among  flowers,  but 
there  is  to  be  observed  a  tendency  in  some  to  carry  the 
insertion  of  the  outer  parts  higher  up.  When  tlie  outer 
parts  arise  from  the  rim  of  an  urn-like  outgrowth  from  the 


Fig.  205.  Flowers  of  Rose  family:  i,  a hypogynons 
flower  of  PotentUla,  sepals,  petals,  and  stamens 
arising  from  beneath  the  head  of  carpels;  5,  a 
perigynous  flower  of  Alcheinilla,  sepals,  petals, 
and  stamens  arising  from  rim  of  nrn-like  pro- 
longation of  the  receptacle,  which  surrounds  the 
carpel  ;  3,  an  epigynons  flower  of  the  common 
apple,  in  which  all  the  parts  seem  to  arise  from 
the  top  of  the  ovary,  two  of  whose  loculi  are 
seen.— After  Focke. 


receptacle,  which  surrounds  the  pistil  or  pistils,  the  flower 
is  said  to  be  perigynous  (Figs.  205,  ^,  206),  meaning  "  around 
the  pistil."  Finally,  the  insertion  is  carried  above  the  ovary, 
and  sepals,  petals,  and  stamens  seem  to  arise  from  the  toj? 
of  the  ovary  (Fig.  205,  5),  such  a  flower  being  epigynous, 
the  outer  parts  appearing  "upon  the  ovary."  In  such  a 
case  the  ovary  does  not  appear  within  the  flower,  but  below 
it  (Figs.  205,  252,  261),  and  the  flower  is  often  said  to  have 
an  "inferior  ovary." 

123.  Apocarpous  to  syncarpous  flowers. — In   the   simpler 
flowers  the  carpels  are  entirely  distinct,  each  carpel  organ- 


226 


PLANT   STRUCTURES 


izing  a  simple  pistil,  a  single  flower  containing  as  many 
pistils  as  there  are  carpels,  as  in  the  buttercups  (Figs. 
200,  202).  Such  a  flower  is  said  to  be  apocarpous,  meaning 
"carpels   separate."     There  is  a   very   strong  tendency. 


FiQ.  206.  Sweet-scented  shrub  (Calycanthus):  A,  tip  of  branch  bearing  flowers;  B, 
section  throiiijh  flower,  showing  numerous  floral  leaves,  stamens,  and  carpels,  and 
also  the  develojiment  of  the  receptacle  about  the  carpels,  making  a  perigynous 
flower. — After  Thiebactlt. 


however,  for  the  carpels  of  a  flower  to  organize  together 
and  form  a  single  compound  pistil.  In  such  a  flower  there 
may  be  several  carpels,  but  they  all  appear  as  one  organ 
(Figs.  195,  C,  197,  198,  D,  199,  B),  and  the  flower  is  said 
to  be  spicarpous,  meaning  "carpels  together." 

124.  Polypetalous  to  s3anpetalous  flowers. — The  tendency 
for  parts  of  the  same  set  to  coalesce  is  not  confined  to  the 
carpels.  Sepals  often  coalesce  (Fig.  208),  and  sometimes 
stamens,  but  the  coalescence  of  petals  seems  to  be  more 
important.  Among  the  lower  forms  the  petals  are  entirely 
separated  (Figs.  199,  A,  202,  203,  207),  a  condition  which 


THE   FLOWER 


227 


has  received  a  variety  of  names,  but 
probably  the  most  common  is  2)oly- 
petalous,  meaning  "petals  many," 
although  eleutheropetalous,  meaning 
"petals  free,"  is  much  more  to  the 
point. 

In  the  highest  Angiosperms,  how- 
ever, the  petals  are  coalesced,  form- 
ing a  more  or  less  tubular  organ 
(Figs.  208-210).  Such  flowers  are 
said  to  be  sympetalous,  meaning 
"petals  united."  The  words  gamo- 
petalous  and  monopetalous  are  also 

much  used,  but  all  three  words  refer  to  the  same  condition 
of  the  flower.     Often  the  sympetalous  corolla  is  difEerenti- 


FiG.  207.  Flower  of  straw- 
berry, showing  sepals,  pet- 
als, numerous  stamens, 
and  head  of  carpels  ;  the 
flower  is  actinomorphic, 
hypogynons,  and  with  no 
coalescence  of  parts.— Af- 
ter Bailey. 


Fig.  208.  A  flower  of  the  tobacco  plant:  «,  a  complete  flower,  showing  the  calyx  with 
its  sepals  blended  below,  the  funnelform  corolla  made  up  of  united  petals,  and  the 
stamens  jnst  showing  at  the  mouth  of  the  corolla  tube;  b.  a  corolla  tube  split  open 
and  showing  the  five  stamens  attached  to  it  near  the  base;  c,  a  syncarpons  pistil 
made  up  of  two  carpels,  showing  ovary,  style,  and  stigma.— After  Stbasbuboer. 


228 


PLANT   STRUCTUEES 


ated  into  two  regions  (Fig.  210,  h),  a  more  or  less  tubular 
portion,  the  tuhe,  and  a  more  or  less  flaring  portion,  the  limb. 

125.  Actinomorphic 
to  zygomorpMc  flow- 
ers.— In  the  simpler 
flowers  all  the  mem- 
bers of  any  one  cycle 
are  alike  ;  the  petals 
are  all  alike,  the 
stamens  are  all  alike, 
etc.  Looking  at  the 
center  of  the  flower, 
all  the  parts  are  re- 
peated about  it  like 
the  parts  of  a  radi- 
ate animal.  Such  a 
flower  is  actinomor- 
pJiic,  meaning  "ra- 
diate," and  is  often 
called  a  "  regular 
flower."  Although 
the  term  actinomor- 
phic strictly  applies  to  all  the  floral  organs,  it  is  especially 
noteworthy  in  connection  with  the  corolla,  whose  changes 
will  be  noted. 


Fig.  209.  Flower  of  morning-glory  (Jpomixa),  with 
sympetalous  corolla  split  open,  showing  the  five 
attached  stamens,  and  the  superior  ovary  with 
prominent  style  and  stigma ;  the  flower  is  hy- 
pogynous,  sympetalous,  and  actinomorphic. — 
After  Mkissner. 


Fig.  210.  A  group  of  sympetalous  flower  forms:  a,  a  flower  of  harebell,  showing  a 
bell-shaped  corolla;  b,  a  flower  of  phlox,  showing  a  tube  and  spreading  limb;  c,  a 
flower  of  dead-nettle,  showing  a  zygomorphic  two-lipped  corolla;  d,  a  flower  of 
toad-flax,  showing  a  two-lipped  corolla,  and  also  a  spur  formed  by  the  base  of  the 
corolla;  e,  a  flower  of  the  snapdragon,  showing  the  two  lips  of  the  corolla  closed. 
—After  Gray. 


THE  FLOWER 


229 


In  many  cases  the  petals  are  not  all  alike,  and  the  radi- 
ate character,  with  its  similar  parts  repeated  about  a  cen- 
ter, is  lost.     In  the 

common    violet,    for  /^  -  ^ 

example,  one  of  the 
petals  develops  a  spur 
(Fig.  211)  ;  in  the 
sweet  pea  the  petals 
are  remarkably  un- 
like, one  being  broad 
and  erect,  two  small- 
er and  drooping 
downward,  and  the 
other  two  much  modi- 
fied to  form  together 
a  boat-like  structure 
which  incloses  the 
sporophylls.  Such  flowers  are  called  zygomorpJiic,  meaning 
"yoke-form,"  and  they  are  often  called  "  irregular  flowers." 

When  zygomorphic  flowers  are  also  sympetalous  the 
corolla  is  often  curiously  shaped.     A  very  common  form 


Fig.  211.  The  pansy  (Viola  tricolor) :  A,  section 
showing  sepals  {I,  I'),  petals  (c)  one  of  which 
produces  a  spur  (cs),  the  flower  being  zygomor- 
phic; B,  mature  fruit  (a  capsule)  and  persistent 
calyx  (A;);  C,  the  three  boat-shaped  valves  of 
the  fruit  open,  most  of  the  seeds  (s)  having 
been  discharged.— After  Sachs. 


Fig.  212.     Flower  of  a  mint  {Mentha  aqnatica):  A,  the  entire  flower,  showing  calyx 
of  united  sepals,  unequal  petals,  stamens,  and  style  with  two  stigma  lobes;  B.  a 
corolla  split  open,  showing  petals  united  and  the  four  stamens  attaclied  to  the 
tube;  the  flower  is  sympetalous  and  zygomorphic— After  Werminq. 
33 


230 


PLANT   STKDCTUKES 


Fig.  213.  Flower  of  a  Labiate  {Teucrlum), 
showing  the  calyx  of  coalesced  sepals, 
the  sympetalous  and  two-lipped  (bilabi- 
ate) corolla  with  three  petals  (middle  one 
largest)  in  the  lower  lip  and  two  small 
ones  in  the  upper,  and  the  stamens  and 
style  emerging  through  a  slit  on  the  up- 
per side  of  the  tube;  a  sympetalous  and 
zygomorphic  flower. — After  Briquet. 


is  the  bilabiate,  or  "two-lipped,"  in  which  two  of  the  petals 
usually  organize  to  form  one  lip,  and  the  other  three  form 

the   other  lip    (Figs.   210, 
B^  c,  d,  e,  212,  213).     The  two 

lips  may  be  nearly  equal, 
the  upper  may  stand  high 
or  overarch  the  lower,  the 
lower  may  project  more  or 
less  conspicuously,  etc. 

126.  Inflorescence.— 
Very  often  flowers  are  soli- 
tary, either  on  the  end  of 
a  stem  or  branch  (Figs. 
231,  236),  or  in  the  axil 
of  a  leaf  (Fig.  258).  But 
such  cases  grade  insensibly  into  others  Avhere  a  definite 
region  of  the  plant  is  set  aside  to  produce  flowers  (Figs. 
253,  260).  Such  a  region  forms  what  is  called  the  inflo- 
rescence. The  various  ways  in  which  flowers  are  arranged 
in  an  inflorescence  have  received  technical  names,  but  they 
do  not  enter  into  our  purpose  here.  They  are  simply  dif- 
ferent ways  in  which  plants  seek  to  display  their  flowers 
so  as  to  favor  pollination  and  seed  distribution. 

There  are  several  tendencies,  however,  which  may  be 
noted.  Some  groups  incline  to  loose  clusters,  either  elon- 
gated (Fig.  260)  or  flat-topped  (Fig.  253)  ;  others  prefer 
large  and  often  solitary  flowers  (Fig.  258)  to  a  cluster  of 
smaller  ones  ;  but  in  the  highest  groups  there  is  a  distinct 
tendency  to  reduce  the  size  of  the  flowers,  increase  their 
number,  and  mass  them  into  a  compact  cluster.  This  ten- 
dency reaches  its  highest  expression  in  tlie  greatest  family 
of  the  Angiosperms,  the  Compositse,  of  which  the  sunflower 
or  dandelion  can  be  taken  as  an  illustration  (Figs.  261, 262), 
in  which  numerous  small  flowers  are  closely  packed  together 
in  a  compact  cluster  which  resembles  a  single  large  flower. 
It  does  not  follow  that  all  very  compact  inflorescences  in- 


THE   FLOWEK  231 

dicate  plants  of  high  rank,  for  the  cat-tail  flag  (Fig.  221) 
and  many  grasses  have  very  compact  inflorescences,  and 
they  are  supposed  to  be  plants  of  low  rank.  It  is  to  be 
noted,  however,  that  the  very  highest  groups  have  settled 
upon  this  as  the  best  type  of  inflorescence. 

127.  Summary. — In  tracing  the  evolution  of  flowers, 
therefore,  the  following  tendencies  become  evident :  (1) 
from  naked  flowers  to  those  with  distinct  calyx  and  corolla  ; 
(2)  from  spiral  arrangement  and  indefinite  numbers  to  cyclic 
arrangement  and  definite  numbers  ;  (3)  from  hypogynous 
to  epigynous  flowers  ;  (-t)  from  apocarpous  to  syncarpous 
pistils  ;  (5)  from  polypetalous  to  sympetalous  corollas  ;  (6) 
from  actinomorphic  or  regular  to  zygomorphic  or  irregular 
flowers  ;  (7)  from  loose  to  compact  inflorescences. 

These  various  lines  appear  in  all  stages  of  advancement 
in  different  flowers,  so  that  it  would  be  impossible  to  deter- 
mine the  relative  rank  in  all  cases.  However,  if  a  flower 
is  naked,  sjjiral,  with  indefinite  numbers,  hypogynous,  and 
apocarpous,  it  would  certainly  rank  very  low.  On  the  con- 
trary, the  flowers  of  the  Compositse  have  calyx  and  corolla, 
are  cyclic,  epigynous,  syncarpous,  sympetalous,  often  zygo- 
morphic, and  are  in  a  remarkably  compact  inflorescence, 
indicating  the  highest  possible  combination  of  characters. 

128.  Flowers  and  insects.  —  The  adaptations  between 
flowers  and  insects,  by  which  the  former  secure  pollination 
and  the  latter  food,  are  endless.  Many  Angiosperm  flowers, 
especially  those  of  the  lower  groups,  are  still  anemophilous, 
as  are  the  Gymnosperms,  but  most  of  them,  by  the  presence 
of  color,  odor,  and  nectar,  indicate  an  adaptation  to  the 
visits  of  insects.  This  wonderful  chapter  in  the  history  of 
plants  will  be  found  discussed,  with  illustrations,  in  Plant 
Relations,  Chapter  Yll. 


CHAPTEK  XIV 


MONOCOTYLEDONS  AND  DICOTYLEDONS 


129.  Contrasting  characters.— The  two  great  groups  of 
Angiosperms  are  quite  distinct,  and  there  is  usually  no  dif- 
ficulty in  recognizing  them.  The  monocotyledons  are 
usually  regarded  as  the  older  and  the  simpler  forms,  and 
are  represented  by  about  twenty  thousand  species.  The 
Dicotyledons  are  much  more  abundant  and  diversified,  con- 
taining about  eighty  thousand  species,  and  form  the  domi- 
nant vegetation  almost  everywhere. 
The  chief  contrasting  characters 
may  be  stated  as  follows  : 

Monocofi/Iedons.  —  (1)  Embryo 
with  terminal  cotyledon  and  lat- 
eral stem-tip.  This  character  is 
practically  without  exception. 

(2)  Vascular  bundles  of  stem 
scattered  (Fig.  214).  This  means 
that  there  is  no  annual  increase  in 
the  diameter  of  the  woody  stems, 
and  no  extensive  branching,  but 
to  this  there  are  some  exceptions. 

(3)  Leaf  veins  forming  a  closed 
system  (Fig.  215,  figure  to  left). 
As  a  rule  there  is  an  evident  set 

of  veins  which  run  approximately  parallel,  and  intricately 
branching  between  them  is  a  system  of  minute  veinlets  not 
readily  seen.     The  vein  system  does  not  end  freely  in  the 
232 


Fig.  214.  Section  of  stem  of 
corn,  showing  the  scattered 
bundles,  indicated  by  black 
dots  in  cross-section,  and  by 
lines  in  longitudinal  section. 
—From  "Plant  Relations." 


MONOCOTYLEDONS   AND   DICOTYLEDONS  233 

margin  of  the  leaf,  but  forms  a  '*  closed  venation,"  so  that 
the  loaves  usually  have  an  even  {entire)  margin.     There 

are  some  notable  exceptions 
to  this  character. 

(4)   Cyclic  flowers  trim- 
crous.    The  "three-parted" 


Fm.  215.  Two  types  of  leaf  venation:  the  figure  to  the  left  is  from  Solomon's  seal, 
a  Monocotyledon,  and  shows  the  principal  veins  parallel,  the  very  minute  cross 
veinlets  being  invisible  to  the  naked  eye;  that  to  the  right  is  from  a  willow,  a 
Dicotyledon,  and  shows  netted  veins,  the  main  central  vein  (midrib)  sending  out 
a  series  of  parallel  branches,  which  are  connected  with  one  another  by  a  network 
of  veinlets. — After  Ettingshausen. 


flowers  of  cyclic  Monocotyledons  are  quite  characteristic, 
but  there  are  some  trimerous  Dicotyledons. 

Dicotijledons. — (1)  Embryo  with  lateral  cotyledons  and 
terminal  stem-tip. 

(2)  Vascular  bundles  of  stem  forming  a  hollow  cylinder 
(Fig.  216,  w).     This  means  an  annual  increase  in  the  diam- 


234 


FLAMT   STKUCTUKES 


Fig.  216.  Section  across  a  young  twig  of 
box  elder,  showing  the  four  stem  regions: 
«,  epidermis,  represented  by  the  heavy 
bounding  line;  c,  cortex;  w,  vascular  cyl- 
inder; }},  pith.— From  "Plant  Relations." 


eter  of  woody  stems  (Fig. 
217,  w),  and  a  possible 
increase  of  the  branch 
system  and  foliage  dis- 
play each  year. 

(3)  Leaf  veins  form- 
ing an  open  system  (Fig. 
215,  figure  to  right). 
The  network  of  smaller 
veinlets  between  the 
larger  veins  is  usually 
very  evident,  especially 
on  the  under  surface  of 
the  leaf,  suggesting  the 
name  "net- veined" 
leaves,  in  contrast  to  the  ''  parallel-veined  "  leaves  of  Mono- 
cotyledons. The  vein  system  ends  freely  in  the  margin  of 
the  leaf,  forming  an  "open  venation."  In  consequence  of 
this,  although  the  leaf 
may  remain  entire,  it 
very  commonly  be- 
comes toothed,  lobed, 
and  divided  in  various 
ways.  Two  main  types 
of  venation  may  be 
noted,  which  influence 
the  form  of  leaves.  In 
one  case  a  single  very 
prominent  vein  {rio) 
runs  through  the  mid- 
dle of  the  blade,  and 
is  called  the  midrib. 
From  this  all  the  mi- 
nor veins  arise  as 
branches  (Figs.  218, 
219),  and  such  a  leaf 


Fia.  217.  Section  across  a  twig  of  box  elder 
three  years  old,  showing  three  annual  rings, 
or  growth  rings,  in  the  vascular  cylinder;  the 
radiating  lines  (m)  which  cross  the  vascular 
region  (w)  represent  the  pith  rays,  the  princi- 
pal ones  extending  from  the  pith  to  the  cor- 
tex (c).— From  "  Plant  Relatione." 


MONOCOTYLEDONS   AND    DICOTYLEDONS 


235 


is  said  to  be  pinnate  or  pinnately  veined,  and  inclines  to 
elongated  forms.  In  the  other  case  several  ribs  of  equal 
prominence  enter  the  blade  and  diverge  through  it  (Fig. 
318).  Such  a  leaf  is  palmate  or  palmately  veined,  and  in- 
.  clines  to  broad  forms. 

(4)   Cyclic   flowers  pentamerous  or  tetramerous.     The 
flowers  ''in  fives"  are  greatly  in  the  majority,  but  some 


Fig.  218.    Leaves  showing  pinnate  and  palmate  branching;  the  one  to  the  left  is  from 
sumach,  that  to  the  right  from  buckeye. — Caldwell. 


very  prominent  families  have  flowers  ''  in  fours."  There 
are  also  dicotyledonous  families  with  flowers  "in  threes/' 
and  some  with  flowers  "  in  twos." 

It  should  be  remembered  that  no  one  of  the  above  char- 
acters, unless  it  be  the  character  of  the  embryo,  should  be 
depended  upon  absolutely  to  distinguish  these  two  groups. 


236  PLANT   STRUCTURES 

It  is  the  combination  of  characters  which  determines  a 
group. 

Monocotyledons 

130.  Introductory. — This  great  group  gives  evidence  of 
several  distinct  lines  of  development,  distinguished  by  what 
may  be  called  the  working  out  of  different  ideas.  In  this 
way  numerous  families  have  resulted — that  is,  groups  of 


Fig.  219.    A  leaf  of  honey  locust,  to  show  twice  pinnate  branching  (bipinnate  leaf  ).— 

Caldwell. 

forms  which  seem  to  belong  together  on  account  of  similar 
structures.  This  similarity  of  structure  is  taken  to  mean 
relationship.  A  family,  therefore,  is  made  up  of  a  group 
of  nearly  related  forms  Opinions  may  differ  as  to  what 
forms  are  so  nearly  related  that  they  deserve  to  consti- 
tute a  distinct  family.  A  single  family  of  some  botanists 
may  be  "  split  up "  into  two  or  more  families  by  others. 
Despite  this  diversity  of  opinion,  most  of  the  families  are 
fairly  well  recognized. 


MONOCOTYLEDONS   AND   DICOTYLEDONS  237 

Within  a  family  there  are  smaller  groups,  indicating 
closer  relationships,  known  as  genera  (singular,  genus). 
For  example,  in  the  great  family  to  which  the  asters  belong, 
the  different  asters  resemble  one  another  more  than  they  do 
any  other  members  of  the  family,  and  hence  are  grouped 
together  in  a  genus  Aster.  In  the  same  family  the  golden- 
rods  are  grouped  together  in  the  genus  Solidago.  The 
different  kinds  of  Aster  or  of  Solidago  are  called  species 
(singular  also  species).  A  group  of  related  species,  there- 
fore, forms  a  genus  ;  and  a  group  of  related  genera  forms  a 
family. 

The  technical  name  of  a  plant  is  the  combination  of  its 
generic  and  specific  names,  the  former  always  being  written 
first.  For  example,  Quercus  alba  is  the  name  of  the  com- 
mon white  oak,  Quercus  being  the  name  of  the  genus  to 
which  all  oaks  belong,  and  alba  the  specific  name  which 
distinguishes  this  oak  from  other  oaks.  No  other  names 
are  necessary,  as  no  two  genera  of  plants  can  bear  the  same 
name. 

In  the  Monocotyledons  about  forty  families  are  recog- 
nized, containing  numerous  genera,  and  among  these 
genera  the  twenty  thousand  species  are  distributed.  It  is 
evident  that  it  will  be  impossible  to  consider  such  a  vast 
array  of  forms,  even  the  families  being  too  numerous  to 
mention.  A  few  important  families  will  be  mentioned, 
which  will  serve  to  illustrate  the  group. 

131.  Pondweeds. — These  are  submerged  aquatics,  found 
in  most  fresh  waters  (some  are  marine),  and  are  regarded 
as  among  the  simplest  Monocotyledons.  They  are  slender, 
branching  herbs,  growing  under  water,  but  often  having 
floating  leaves,  and  sending  the  simple  flowers  or  flower 
clusters  above  the  surface  for  pollination  and  seed-distri- 
bution. The  common  pondweed  (Potamogeton)  contains 
numerous  species  (Fig.  320),  while  Kaias  (naiads)  and 
Zannichellia  (horned  pondweed)  are  common  genera  in 
ponds  and  slow  waters. 


238 


TLAJs^T   STRUCTURES 


The  simple  character  of  these  forms  is  indicated  by  their 
aquatic  habit  and  also  by  their  flowers,  which  are  mostly 
naked  and  with  few  sporophylls.  A  flower  may  consist  of 
a  single  stamen,  or  a  single  carpel ;  or  there  may  be  several 
stamens  and  carpels  associated,  but  without  any  coalescence 
(Fig.  220,  B). 

In  the  same  general  line  with  the  pondweeds,  but  with 
more  complex  flowers,  are  the  genera   Sagittaria  (arrow- 


PiG.  220.  Pondweed  {Potamogeton):  A,  branch  with  cUister  (spike)  of  simple  flowers, 
showing  also  the  broad  floating  leaves  and  the  narrow  submerged  ones;  B,  a  sin- 
gle flower,  showing  the  inconspicuous  perianth  lobes  (c),  the  short  stamens  (a), 
and  the  two  short  styles  with  conspicuous  stigmatic  surfaces.— J^  after  Reiohen- 
bach;  B  after  Le  Maout  and  Dbcaisnb. 


Fig.  221.  Cat-tails  ( Typha),  ehowinp;  the  dense  spikes  of  very  simple  flowers,  each 
showing  two  regions,  the  lower  the  pistillate  flowers,  the  upper  the  staminate. — 
From  "  Field,  Forest,  and  Wayside  Flowers." 


240 


PLANT   STRUCTUEES 


leaf)  and  Alis7na  (water-plantain),  in  which  there  is  a  dis- 
tinct calyx  and  corolla.  The  genus  Typlia  (cat-tail)  is  also 
an  aquatic  or  marsh  form  of  very  simple  type,  the  flow- 
ers being  in  dense 
cylindrical  clusters 
(spikes),  the  upper 
flowers  consisting  of 
stamens,  the  lower  of 
carpels,  thus  forming 
two  very  distinct  re- 
gions of  the  spike 
(Fig.  221). 

132.  Grasses. — 
This  is  one  of  the 
largest  and  probably 
one  of  the  most  use- 
ful groups  of  plants, 
as  well  as  one  of  the 
most  peculiar.  It  is 
world-wide  in  its  dis- 
tribution, and  is  re- 
markable in  its  dis- 
play of  individuals, 
often  growing  so 
densely  over  large 
areas  as  to  form  a 
close  turf.  If  the 
grass -like  sedges  be 
associated  with  them 
there  are  about  six 
thousand  species, 
representing  nearly 
one  third  of  the  Mon- 
ocotyledons. Here 
belong  the  various 
cereals,  sugar  canes. 


Fig.  222.  A  common  meadow  graBS  {Festuca) :  A, 
portion  of  flower  cluster  (spikelet),  showing  the 
bracts,  in  the  axils  of  two  of  which  flowers  are 
exposed  ;  B,  a  single  flower  with  its  envelop- 
ing bract,  showing  three  stamens,  and  a  pistil 
whose  ovary  bears  two  style  branches  with  much 
branched  stigmas.— After  Strasburger. 


MONOCOTYLEDONS   AND    DICOTYLEDONS  241 

bamboos,  and  pasture  grasses,  all  of  them  immensely  use- 
ful plants. 

The  flowers  are  very  simple,  having  no  evident  perianth 
(Fig.  323).  Most  commonly  a  flower  consists  of  three  sta- 
mens, surrounding  a  single  carpel,  whose  ovary  ripens  into 
the  grain,  the  characteristic  seed-like  fruit  of  the  group. 
The  stamens,  however,  may  be  of  any  number  from  one  to 
six.  The  flowers,  therefore,  are  naked,  with  indefinite  num- 
bers, and  hypogynous,  indicating  a  comparatively  simple 
type.    It  is  also  noteworthy  that  the  group  is  aneniophilous. 

One  of  the  noteworthy  features  of  the  group  is  the 
prominent  development  of  peculiar  leaves  {bracts)  in  con- 
nection with  the  flowers.  Each  flower  is  completely  pro- 
tected or  even  inclosed  by  one  of  these  bracts,  and  as  the 
bracts  usually  overlap  one  another  the  flowers  are  invisible 
until  the  bracts  spread  apart  and  permit  the  long  dangling 
stamens  to  show  themselves.  These  bracts  form  the  so- 
called  ''chaff"  of  wheat  and  other  cereals,  where  they 
persist  and  more  or  less  envelop  the  grain  (ripened  ovary). 
As  they  are  usually  called  glumes,  the  grasses  and  sedges 
are  said  to  be  glumaceoiis  plants. 

Grasses  are  not  always  lowly  plants,  for  in  the  tropics 
the  bamboos  and  canes  form  growths  that  may  well  be 
called  forests.  The  grasses  constitute  the  family  GraminecB, 
and  the  sedges  the  family  Cyperacem. 

133.  Palms. — More  than  one  thousand  species  of  palms 
are  grouped  in  the  family  Palmacew.  These  are  the  tree 
Monocotyledons,  and  are  very  characteristic  of  the  tropics, 
only  the  palmetto  getting  as  far  north  as  our  Gulf  States. 
The  habit  of  body  is  like  that  of  tree-ferns  and  Cycads,  a 
tall  unbranched  columnar  trunk  bearing  at  its  summit  a 
crown  of  huge  leaves  which  are  pinnate  or  palmate  in  char- 
acter, and  often  splitting  so  as  to  appear  lobed  or  comi)ound 
(Figs.  233,  324). 

The  flower  clusters  are  usually  very  large  (Fig.  323), 
and  each  cluster  at  first  is  inclosed  in  a  huge  bract,  which 


Fig.  2a3.  A  date  palm,  showing  the  unbranched  columnar  trunk  covered  with  old  leaf 
bases,  and  with  a  cluster  of  huge  pinnate  leaves  at  the  top,  only  the  lowest  por- 
tions of  which  are  shown ;  two  of  the  very  heavy  fruit  clusters  are  also  shown. — 
From  "  Plant  Relations." 


MONOCOTYLEDONS   AND   DICOTYLEDONS 


243 


is  often  hard.  Usually  a  perianth  is  present,  but  with  no 
differentiation  of  calyx  and  corolla,  and  the  flower  parts  are 
quite  definitely  in  "  threes,"  so  that  the  cyclic  arrangement 
with  the  characteristic  Monocotyledon  number  appears. 


Fio. 


234.    A  fan  palm,  with  low  stem  mid  .  rown  of  large  palmate  leaves,  which  have 
split  so  as  to  appear  palmately  bruuched.— From  ••  Plant  Relations." 


134.  Aroids. — This  is  a  group  of  nearly  one  thousand 
species,  most  of  them  belonging  to  the  family  Aracecs.  In 
our  flora  the  Indian  turnip  or  Jack-in-the-pulpit  {AriscBma) 
(Fig.  225),  sweetflag  (Acorns),  and  skunk-cabbage  {Symplo- 
carpus),  may  be  taken  as  representatives ;  while  the  culti- 
vated Calla-lily  is  perhaps  even  better  known.  The  great 
display  of  aroids,  however,  is  in  the  tropics,  where  they  are 
endlessly  modified  in  form  and  structure,  and  are  erect,  or 
climbing,  or  epiphytic. 


244 


PLANT   STRUCTURES 


The  flowers  are  usually  very  simple,  often  being  naked, 
with  two  to  nine  stamens,  and  one  to  four  carpels  (Fig. 


Fig.  225.    Jack-in-the-pulpit  (Arismma).  showing  the  overarching  spathes;   in  one 
case  a  side  view  shows  the  naked  tip  of  the  projecting  spadix.— After  Atkinson. 

197).     They  are  inconspicuous  and  closely  set  upon  the 
lower  part  of  a  fleshy  axis,  which  is  naked  above  and  often 


MONOCOTYLEDONS  AND  DICOTYLEDONS 


245 


modified  in  a  remarkable  way  into  a  club-shaped  or  tail-like 
often  brightly  colored  affair.  This  singular  flower-cluster 
with  its  fleshy  axis  is  called  a  spaclix.  The  flowers  often 
include  but  one  sort  of  sporophyll,  and  staminate  and 
pistillate  flowers  hold  different  positions  upon  the  spadix 
(Fig.  226). 

The  spadix  is  enveloped  by  a  great  bract,  which  sur- 
rounds and  overarches  like  a  large  loose  hood,  and  is  called 
the  spatlie.  The  spathe  is  exceedingly 
variable  in  form,  and  is  often  conspic- 
uously colored,  forming  in  the  Calla- 
lily  the  conspicuous  white  part,  within 
which  the  spadix  may  be  seen,  near  the 
base  of  which  the  flowers  are  found. 
In  Jack-in-the-pulpit  (Fig.  225)  it  is 
the  overarching  spathe  which  suggests 
the  "  pulpit."  The  spadix  and  spathe 
are  the  characteristic  features  of  the 
group,  and  the  spathe  is  variously 
modified  in  form,  structure,  and  color 
for  insect  pollination,  as  is  the  peri- 
anth of  other  entomophilous  groups. 

Aroids  are  further  peculiar  in  hav- 


ing broad  net-veined  leaves  of  the  Di- 


FiG.  226.  Spadix  of  an 
Arum,  with  spathe  re- 
moved, showing  cluster 
of  naked  pistillate  flow- 
ers at  base,  just  above 
a  cluster  of  staminate 
flowers,  and  the  club- 
shaped  tip  of  the  spa- 
dix.—After  WOSSIDLO. 


cotyledon  type.  Altogether  they  form 
a  remarkably  distinct  group  of  Mon- 
ocotyledons. 

135.  Lilies. — The  lily  and  its  allies  are  usually  regarded 
as  the  typical  Monocotyledon  forms.  The  perianth  is 
fully  developed,  and  is  very  conspicuous,  either  undifferen- 
tiated or  with  distinct  calyx  and  corolla,  and  the  flower  is 
well  organized  for  insect  pollination.  The  flowers  are  either 
solitary  or  few  in  a  cluster  and  correspondingly  large,  or  in 
more  compact  clusters  and  smaller.  In  any  event,  the 
perianth  is  the  conspicuous  thing,  rather  than  spathes  or 

glumes. 

34 


246 


PLANT   STRUCTUEES 


In  the  general  lily  alliance,  composed  of  eight  or  nine 
families,  there  are  more  than  four  thousand  species,  repre- 
senting about  one  fifth  of  all  the  Monocotyledons,  and  they 
are  distributed  everywhere.  They  are  almost  all  terrestrial 
herbs,  and  are  prominently  geopMlous  ("earth -lovers") — 

that  is,  they  develop 
bulbs,  rootstocks,  etc., 
which  enable  them  to 
disappear  from  above 
the  surface  during  un- 
favorable conditions 
(cold  or  drought),  and 
then  to  reappear  rap- 
idly upon  the  return 
of  favorable  conditions 
(Figs.  227,  228,  231, 
233). 

In  the  regular  lily 
family  {Liliacece)  the 
flowers  are  hypogy- 
nous  and  actinomor- 
phic  (Fig.  231),  the 
six  perianth  parts  are 
mostly  alike  and  some- 
times sympetalous  (as 
in  the  lily-of-the-val- 
ley,  hyacinth,  easter 
lily)  (Figs.  201,  229), 
the  stamens  are  usu- 
ally six  (two  sets), 
and  the  three  carpels  are  syncarpous  (Figs.  204,  230). 
This  is  a  higher  combination  of  floral  characters  than 
any  of  the  preceding  groups  presents.  Hypogyny  and 
actinomorphy  are  low,  but  a  conspicuous  perianth,  syn- 
carpy,  and  occasional  sympetaly  indicate  considerable  ad- 
vancement. 


Fig.  227.  Wake-robin  {Trillium),  showing  root- 
stock,  from  which  two  branches  arise,  each  bear- 
ing a  cycle  (whorl)  of  three  leaves  and  a  single 
trimerons  flower.— After  Atkinson. 


MONOCOTYLEDONS  AND  DICOTYLEDONS 


247 


In  the  amaryllis  family  {Amarijllidacece),  a  higher  fam- 
ily of  the  same  general  line,  represented  by  species  of  Nar- 
cissus (jonquils,  daffodils,  etc.).  Agave,  etc.,  the  flowers 
are  distinctly  epigynous. 


Fig  2^.  Star-of -Bethlehem  ( Ornithogalitm) :  a,  entire  plant  with  tnberons  base  and 
tnmerous  flowers;  b.  a  single  flower;  c,  portion  of  flower  showing  relation  of 
parts,  perianth  lobes  and  stamens  arising  from  beneath  the  prominent  ovary  (hy- 
pogynous);  d,  mature  fruit;  e.  section  of  the  syncarpous  ovary,  showing  the  three 
carpels  and  loculi.— After  ScHisirER. 

In  the  iris  family  (Iridacece),  the  most  highly  specialized 
family  of  the  lily  line,  and  represented  by  the  various  spe- 


Fig.  say.    The  Japan  lily,  showing  a  tubular  puriaiuh,  the  parts  of  the  perianth 
distinct  above.— From  "  Field,  Forest,  and  Wayside  Flowers." 


MONOCOTYLEDONS  AND  DICOTYLEDONS 


249 


cies  of  Iris  (flags)  (Fig.  232),  Crocus^  Gladiolus  (Figs.  233, 
234),  etc.,  the  flowers  are  not  only  epigynons,  but  some  of 
them  are  zygomorphic. 
When  a  plant  has 
reached  both  epigyny 
and  zygomorphy  in  its 
flowers,  it  may  be  re- 
garded as  of  high  rank. 

136.  Orchids.— In 
number  of  species  this 
{Orchidacecs)  is  the 
greatest  family  among 
the  Monocotyledons, 
the  species  being  vari- 
ously estimated  from 
six  thousand  to  ten 
thousand,  representing 
between  one  third  and 
one  half  of  all  known 

Monocotyledons.  In  display  of  individuals,  however,  the 
orchids  are  not  to  be  compared  with  the  grasses,  or  even 
with  lilies,  for  the  various  species  are  what  are  called  "rare 
plants " — that  is,  not  extensively  distributed,  and  often 
very  much  restricted.  Although  there  are  some  beautiful 
orchids  in  temperate  regions,  as  species  of  Habenaria  (rein- 
orchis)  (Fig.  235),  Pogonia^  Calopogoti,  Ckdyjpso^  (Jypripe- 
dium  (lady-slipper,  or  moccasin  flower)  (Fig.  236),  etc., 
by  far  the  greatest  display  and  diversity  are  in  the  tropics, 
where  many  of  them  are  brilliantly  floAvered  epiphytes 
(Fig.  237). 

Orchids  are  the  most  highly  specialized  of  Monocoty- 
ledons, and  their  brilliant  coloration  and  bizarre  forms  are 
associated  with  marvelous  adaptation  for  insect  visitation 
(see  Plant  Relations^  pp.  134,  135).  The  flowers  are  epigy- 
nous  and  strongly  zygomorphic.  One  of  the  petals  is  re- 
markably modified,   forming  a  conspicuous   Up   which   is 


Fig.  230.  Diagrammatic  cross-section  of  ovary 
of  Liliiim  PhUadelphiciim,  showing  the  three 
loculi,  in  each  of  which  are  two  ovules  (mega- 
sporangia);  ,4,  ovule;  i>,  integuments;  C,  nu- 
cellus  ;  D,  embryo-sac  (megaspore). — Cald- 
well. 


II    |i   III!  l|l—WWHilliMIIII    Ml 


PiQ.  231.  The  common  dog-tooth  violet,  showing  the  large  mottled  leaves  and  con- 
spicuous flowers  which  are  sent  rapidly  above  the  surface  from  the  subterranean 
bulb  (see  cut  w.  the  left  lower  corner),  also  some  petals  and  stamens  and  the  pistil 
dissected  out.— From  "  Plant  Relations." 


MONOCOTYLEDONS   AND   DICOTYLEDONS 


251 


modified  in  a  great  variety  of 
ways,  and  a  prominent,  often 
very  long,  spur,  in  the  bottom  of 
which  nectar  is  secreted,  which 
must  be  reached  by  the  proboscis 
of  an  insect  (Fig.  235).  The 
stamens  are  reduced  to  one  or 
two,  and  welded  with   the   style 


Fig.  233.  Flower  of  flag  {Iris), 
showing  some  of  the  sepals 
and  petals,  one  of  the  three 
stamens,  and  the  distinctly  in- 
ferior ovary,  being  an  epigy- 
nous  flower. — After  Gray. 


Fig.  234.  Flower  cluster  of  Gla- 
dlohis,  showing  somewhat  zygo- 
morphic  flowers.— Caldwell. 


Fig.  2.33.  Gladiolus,  showing  tuberous  subter- 
ranean stem  from  which  roots  descend,  grass- 
like  leaves,  and  somewhat  zygomorphic  flow- 
ers.—After  Reichenbach. 


252 


PLANT   STRUCTURES 


and  stigmatic  surface  into  an  indistinguishable  mass  in 
the  center  of  the  flowers.  The  pollen-grains  in  each  sac 
are  sticky  and  cohere  in  a  club-shaped  mass  {pollinium), 
which  is  pulled  out  and  carried  to  another  flower  by  the 


Fig.  235.  A  flower  of  an  orchid  (Habena- 
ria):  at  1  the  complete  flower  is  shown, 
with  three  sepals  behind  and  three  pet- 
als iu  front,  the  lowest  one  of  which  has 
developed  a  long  strap-sha])ed  portion 
(lip)  and  a  still  longer  spur  portion,  the 
opening  to  which  is  seen  at  the  base  of 
the  strap,  and  behind  the  spur  the  long 
inferior  ovary  (epigynous  character)  ; 
the  two  pollen  sacs  of  the  single  stamen 
are  seen  in  the  center  of  the  flower,  di- 
verging downward,  and  between  them 
stretches  the  stigma  surface  ;  the  rela- 
tion between  pollen  sacs  and  stigma  sur- 
face is  shown  in  -^  ;  within  each  pollen 
sac  is  a  mass  of  sticky  pollen  (pollini- 
um),  ending   below    in   a  sticky  disk, 

which  may  be  seen  in  1  and  ;? ;  in  rf  a  pollen  mass  (a)  is  shown  sticking  to  each 

eye  of  a  moth.— After  Geat. 

visiting  insect.  The  whole  structure  indicates  a  very 
highly  specialized  type,  elaborately  organized  for  insect 
pollination. 

Another  interesting  epigynous  and  zygomorphic  trop- 
ical group,  but  not  so  elaborate  as  the  orchids,  is  repre- 
sented by  the  cannas  and  bananas  (Fig.  120),  common  in 
cultivation  as  foliage  plants,  and  the  aromatic  gingers. 

From  the  simple  pondweeds  to  the  complex  orchids  the 
evolution  of  the  Monocotyledons  has  proceeded,  and  be- 
tween them  many  prominent  and  successful  families  have 
been  worked  out. 


Fig.  23C.     A  clump  of  lady-slippers  (Cypripedium),  showiiij,'  the  luibit  of  the  plant 
and  the  general  structure  of  the  zygomorphic  flower.— After  Gibson. 


254 


PLANT   STRUCTUKES 


Fig.  SJ37.    A  group  of  orchids  ( Cattleya),  showing  the  very  zygomorphic  flowers,  the 
lip  being  well  shown  in  the  flower  to  the  left  (lowest  petal).— Caldwell. 


Dicotyledons 

137.  Introductory. — Dicotyledons  form  the  greatest  group 
of  plants  in  rank  and  in  numbers,  being  the  most  highly 
organized,  and  containing  about  eighty  thousand  species. 
They  represent  the  dominant  and  successful  vegetation  in 
all  regions,  and  are  especially  in  the  preponderance  in  tem- 
perate regions.  They  are  herbs,  shrubs,  and  trees,  of  every 
variety  of  size  and  habit,  and  the  rich  display  of  leaf  forms 
is  notably  conspicuous. 

Two  great  groups  of  Dicotyledons  are  recognized,  the 
ArcMchlaynydecB  and  the  Sympetal,m.  In  the  former  there 
is  either  no  perianth  or  its  parts  are  separate  (polypeta- 
lous)  ;  in  the  latter  the  corolla  is  sympetalous.  The  Archi- 
chlamydeae  are  the  simpler  forms,  beginning  in  as  simple  a 
fashion  as  do  the  Monocotyledons ;  while  the  Sympetalae 


MONOCOTYLEDONS   AND   DICOTYLEDONS 


255 


are  evidently  derived  from  them  and  become  the  most 
highly  organized  of  all  plants.  The  two  groups  each  con- 
tain about  forty  thousand  species,  but  the  Archichlamydeas 
contain  about  one  hundred  and  sixty  families,  and  the 
Sympetalge  about  fifty. 

To  present  over  two  hundred  families,  containing  about 
eighty  thousand  species,  is  clearly  impossible,  and  a  very 
few  of  the  prominent  ones  will  be  selected  for  illustrations. 

ArcMcJilamydem 

138.  Poplars  and  their  allies. — This  great  alliance  repre- 
sents nearly  five  thousand  species,  and  seems  to  form  an 
isolated  group.  It  is  a  notable  tree  assemblage,  and  appar- 
ently the  most  primitive  and  ancient  group  of  Dicotyledons, 
containing  the  most  important  deciduous  forest  forms  of 


r 


'^. 


-=SJ35:^*S««J£..<A^^ 


Fig.  238.    An  oak  in  winter  condition.— From  "  Plant  Relations." 


256 


PLANT   STEUCTUKES 


temperate  regions,  for  here  belong  the  oak  (Fig.  238),  hick- 
ory, walnut,  chestnut,  beech,  poplar,  birch,  elm  (Figs.  198, 
239),  willow  (Fig.  240),  etc.  The  primitive  character  is  in- 
dicated not  merely  by  the  floral  structures,  but  also  by  the 
general  anemophilous  habit. 

In  the  poplar  {Populns)  and  its  allied  form,  the  willow 
(Salix),  the  flowers  are  naked  and  hypogynous  (Fig.  196), 


Fie.  239.    An  elm  in  foliai; 


-From  "Plant  Relations." 


MONOCOTYLEDONS  AND  DICOTYLEDONS 


257 


the  stamens  are  indefinite  in  number  (two  to  thirty),  and 
the  pistil  is  syncarpous  (two  carpels).     The  stamens  and 


Fig.  240.    Flower  clusters  of  willow  (aments);  that  to  the  left  is  pistillate,  the  other 
staminate. — After  Warming. 

pistils  are  not  only  separated  in  different  flowers,  but  u23on 
different  plants,  some  plants  being  staminate  and  others 
pistillate  (Fig.  240).  The  flowers  are  clustered  upon  a  long 
axis,  and  each  one  is 
protected  by  a  promi- 
nent bract.  It  is  these 
scaly  bracts  which 
give  character  to  the 
cluster,  which  is  called 
an  anient  or  catkin, 
and  the  plants  which 
produce  such  clusters 
are  said  to  be  amenta- 
ceous. These  aments 
of  poplars,  "pussy 
willows,"  and  the 
alders  and  birches  are 
very  familiar  objects 
(Figs.  240,  241). 


Fig.  241.  Aments  of  alder  (Alm/s) :  a,  branch 
with  staminate  aments  (n),  pistillate  aments 
(/«),  and  a  young  bud  {k)\  b.  pistillate  ament  at 
time  of  discharging  seeds,  showing  the  promi- 
nent bracts.— After  Warming. 


258 


PLANT   STKUCTURES 


The  only  advanced  character  in  the  flowers  as  described 
above  is  tlie  syncarpous  pistil,  but  in  the  great  allied  pepper 
family  (Piperacece)  of  the  tropics,  with  its  one  thousand 
species,  and  most  nearly  represented  in  our  flora  by  the 


Pig.  242.  Ovule  of  hornhe&m  (Carpinus),  showing  chalazogamy:  m,  the  micropyle; 
pi,  the  pollen  tube,  which  may  be  traced  to  its  entrance  into  the  embryo-sac  at  its 
antipodal  end,  and  thence  upward  through  the  sac  toward  the  egg.— After  Mart 

EWART. 


lizard-tail  {Saururus)  of  the  swamps  (Fig.  195),  the  flowers 
are  not  merely  naked,  but  also  apocarpous,  and  the  whole 
structure  is  much  like  that  of  the  simplest  Monocotyle- 


MONOCOTYLEDONS   AND   DICOTYLEDONS  259 

dons.  The  peppers  seem  to  represent  the  simplest  of  the 
Dicotyledons,  and  this  great  line  may  have  begun  with 
some  such  forms. 

A  very  interesting  fact  in  connection  with  the  fertiliza- 
tion of  certain  amentaceous  plants  has  been  discovered. 
In  birch,  alder,  walnut,  hornbeam,  and  some  others,  the 
pollen-tube  does  not  enter  the  ovule  by  way  of  the  micro- 
pyle,  but  pierces  through  in  the  region  of  the  base  of  the 
ovule  and  so  penetrates  to  the  embryo-sac  (Fig.  243).  As 
the  region  of  the  ovule  where  integument  and  nucellus  are 
not  distinguishable  is  called  the  chalaza,  this  phenomenon 
is  known  as  chalazogamy,  meaning  ''fertilization  through 
the  chalaza." 

139.  Buttercups  and  their  allies. — This  is  a  great  assem- 
blage of  terrestrial  herbs,  including  nearly  five  thousand 
species,  and  is  thought  by  many  to  be  the  great  stock  from 
which  most  of  the  higher  Dicotyledons  have  been  derived- 
The  alliance  includes  the  water-lilies,  buttercups,  and  pop- 
pies, the  specialized  mustards,  and  certain  notable  tree 
forms,  as  magnolias,  custard-apples,  and  the  tropical  laurels 
with  one  thousand  species  represented  in  our  flora  only 
by  the  sassafras.  Here  also  is  the  strange  group  of  "car- 
nivorous" plants  {Sarracenia,  D7'osera,  Dionma,  etc.).  The 
group  is  distinctly  entomophilous,  in  striking  contrast  with 
the  preceding  one. 

Taking  the  buttercup  {Ranunculus)  as  a  type  (Fig.  202), 
the  flower  is  hypogynous,  the  calyx  and  the  corolla  are  dis- 
tinctly differentiated  and  actinomorphic,  and  adapted  for 
insect-pollination,  but  the  spiral  arrangement  and  indefinite 
numbers  are  very  apparent,  notably  in  connection  with  the 
apocarpous  pistils,  which  are  very  numerous  upon  a  promi- 
nent receptacle,  but  involving  more  or  less  all  the  parts. 
The  stamens  are  also  very  numerous  (Figs.  200,  243,  244). 
In  the  water-lilies  the  petals  and  stamens  are  indefinitely 
numerous  (Fig.  203),  and  in  the  poppies  there  is  no  definite 
number.     In  many  of  the  forms,  however,  in  connection 


Fig.  243.  Marsh  marigold  (  Caltha),  a  member  of  the  Buttercup  famil.v,  aNo  showing 
floral  diagram,  in  which  the  floral  leaves  are  five,  but  the  stamens  and  apocarpous 
pistils  are  indefinitely  numerous.— After  Atkinson. 


Fig.  '244.  Zygomorphic  flower  of  larkspur 
{Delphinium), yviWi  sepals  removed,  show- 
ing two  petals  with  prominent  spurs,  and 
numerous  stamens. — After  Baillon. 


Fig.  245.  Diagram  of  the  zygomorphic 
flower  of  larkspur  (Delphinium),  show- 
ing the  spur  developed  by  a  sepal  and 
inclosing  the  two  petal  spurs. — After 
Baillon. 


MONOCOTYLEDONS   AND   DICOTYLEDONS 


261 


with  one  or  more  of  the  parts,  the  Dicotyl  number  (five) 
appears  (Figs.  243,  245),  but  with  no  special  constancy. 

In  certain  genera  of  the  buttercup  family  {Ranuncula- 
cew)  zygomorphy  appears,  as  in  the  larkspur  {DelpMnium) 
with  its  spurred  petals  and  sepals  (Figs.  244,  245),  and  the 
monkshood  {Aconitum)  with  its  hooded  sepal ;  and  in  the 


Fig.  246.  The  common  cabbage  (Brassica).  a  member  of  the  mustard  family:  A, 
flower  chister,  showing  buds  at  tip,  open  flowers  below  with  four  spreading  petals, 
and  forming  pods  below;  I},  mature  pod,  with  the  persistent  style;  C,  pod  opening 
by  two  valves,  and  showing  seeds  attached  to  the  false  partition. — After  Warming. 


water-lily  family  {NympJicBacece)  and  poppy  family  {Papa- 
veracece)  syncarpy  appears.     In  this  alliance,  also,  belong 
the  sweet-scented  shrubs  (Cali/cantJins),  with  their  perigy- 
nous  flowers  containing  numerous  parts  (Fig.  206). 
35 


2G2 


PLANT   STRUCTURES 


Fig.  247.  Diagram  of  crucifer 
flower,  showing  the  relations 
of  parts  ;  four  sepals,  four 
petals,  six  stamens,  and  one 
carpel  with  a  false  partition. 
—After  Wakmino. 


The  most  specialized  large  group  in  this  alliance  is 
the  mustard  family  {Cruciferm),  with  twelve  hundred 
species,  to  which  belong  the  mustards,  cresses,  shep- 
herd's purse,  peppergrass,  radish,  cabbage  (Fig.  246),  etc. 
The  sepals  are  four  in  two  sets,  the 
petals  four  in  one  set,  the  stamens 
six  with  two  short  ones  in  an  outer 
set  and  four  long  ones  in  an  inner 
set,  and  one  pistil  whose  ovary  be- 
comes divided  into  two  loculi  by 
what  is  called  a  "false  partition" 
(Figs.  246,  C\  247),  and  usually  be- 
comes an  elongated  pod  (Fig.  246, 
A^  B).  This  specialized  structure 
of  the  flower  distinctly  marks  the 
family,  whose  name  is  suggested 
by  the  fact  that  the  four  spreading 
petals  often  form  a  Maltese  cross  (Fig.  246,  A).  The  pecul- 
iar stamen  character,  four  long  and  two  short  stamens,  is 
called  tetradynamous  ("four  strong"). 

140.  Roses. — This  family  {Rosacece)  of  one  thousand 
species  is  one  of  the  best  known  and  most  useful  groups  of 
the  temperate  regions.  In  it  are  such  forms  as  Spir(ea, 
five-finger  {Poten- 
tilla),  strawberry 
{Fragaria)  (Figs. 
191,  207),  raspberry 
(Fig.  248),  and 
blackberry  {R2i- 
bus),  rose  {Rosa), 
hawthorn  ( CratcB- 
gus),  apple,  and 
pear  {Pirns)  (Fig. 
249),  plum,  cherry, 
almond,  and  peach 
{Prunus). 


Fig.  248.  The  common  raspberry:  the  figure  to  the 
left  showing  flower-stalk,  calyx,  old  stamens 
(«),  and  prominent  receptacle,  from  which  the 
"fruit"  (a  cluster  of  small  stone  fruits,  each 
representing  a  carpel)  has  been  removed. — After 
Bailey. 


MONOCOTYLEDONS   AND   DICOTYLEDONS 


2G3 


Many  of  the  true  roses  have  a  strong  resemblance  (Fig. 
307)  to  the  buttercups  {Ranimculus),  with  their  hypogy- 
nous  reguhir  flowers,  and  indefinite  number  of  stamens  and 
carpels,  but  the  sepals  and  petals  are  much  more  frequently 
five,  the  Dicotyl  number  being  better  established.      Tlie 


Flo.  249.  The  common  pear  (Piri/s  communis),  showing  branch  with  flowers  (J),  sec- 
tion of  a  flower  {2)  showing  its  epigynoiis  character,  section  of  fruit  (3)  showing 
the  thickened  calyx  outside  of  the  ovary  or  "core"  (indicated  by  dotted  outline), 
and  flower  diagram  (U)  showing  all  the  organs  in  fives  except  the  stamens.  -After 

WOSSIDLO. 


whole  family  remains  actinomorphic,  but  perigyny  and 
epigyny  appear  in  certain  forms  (Fig.  205),  giving  rise  to 
tlie  peculiar  fruit  (pome)  of  apples  and  pears  (Fig.  249),  in 
which  tlie  calyx  and  ovary  ripen  together.  Another  spe- 
cialized group  of  roses  is  that  which  develops  the  stone- 


204 


PLANT   STRUCTUKES 


fruits    {drupes),   as   apricots,   peaches   (Fig.  189),   plums, 
cherries. 

141.  Legumes. — This  is  far  the  greatest  family  {Legumi- 
noH(e)  of  the  Arcliiclilamydeas,  containing  ahout  seven  thou- 
sand species,  distributed  everywhere  and  of  every  habit.  It 
is  the  great  zygomorphic  group  of  the  Archichlamydese, 
being  elaborately  adapted  to  insect  pollination.     The  more 


Fig.  250.  A  legume  plant  (Lotus),  showing  flowering  branch  (1),  a  single  flower  (3) 
showing  zygomorphic  corolla,  the  cluster  of  ten  stamens  (,3)  which  with  the  carpel 
is  included  in  the  keel,  the  solitary  carpel  (i)  which  develops  into  the  pod  or  le- 
gume (5),  the  petals  {(!)  dissected  apart  and  showing  standard  (a),  wings  (b),  and 
the  two  lower  petals  (c)  which  fold  together  to  form  the  keel,  and  the  floral  dia- 
gram (7).— After  Wossidlo. 


primitive  forms  of  the  Leguminoste,  the  mimosas,  acacias 
(Fig.  251),  etc.,  very  much  resemble  true  roses  and  the  but- 
tercups, with  their  hypogynous  regular  flowers  and  nu- 
merous stamens,  but  the  vast  majority  are  Pcq)iUo  forms 
with  very  irregular  (zygomorphic)  flowers  and  few  stamens 


MONOCOTYLEDONS   AND   DICOTYLEDONS 


265 


(Fig.  250).  The  petals  are  very  dissimilar,  the  upper  one 
{siandard)  being  the  largest,  and  erect  or  spreading,  the  two 
lateral  ones  (wu/gs)  oblique  and  descending,  the  two  lower 
ones  coherent  by  their  edges  to  form  a  projecting  boat-shaped 
body  (keel),  which 
incloses  the  sta- 
mens and  pistil. 
From  a  fancied  re- 
semblance to  a  but- 
terfly such  flowers 
are  said  to  be  papil- 
io7iaceous. 

The  whole  fam- 
ily is  further  char- 
acterized by  the  sin- 
gle carpel,  which 
after  fertilization 
develops  a  pod 
(Fig.  250, 5),  which 
often  becomes  re- 
markably large  as 
compared  with  the 
carpel.  It  is  this 
peculiar  pod  {le- 
gume) which  has 
given  to  the  family 
its  technical  name 
Leguminosm  and 
the  common  name 
"  Legumes." 

Well-known  members  of  the  family  are  lupine  {Liijn- 
nus),  c\o\e\'  {TrifoHum),  locust  {Rohinia),  Wistaria,  pea 
{Pisum),  bean  {Phaseolus),  tragacanth  {Astragalus),  vetch 
{Vicia),  redbud  {Cerci^),  senna  {Cassia),  honey-locust 
{Gleditschia),  indigo  {Indigofera),  sensitive-plants  {Acacia, 
Mimosa,  etc.)  (Fig.  251),  etc. 


^,^y'    ^</ti« 


Fig.  251.  A  sensitive-plant  {Acacia),  showing 
flowers  with  inconspicuous  petals  and  very 
merous  stamens,  and  the  pinriately  branched 
sitive  leaves. — After  Meteu  and  Schumann. 


the 
nu- 
6cn- 


266 


PLANT   STRUCTURES 


142.  Umbellifers. — This  is  the  most  highly  organized 
family  ( Umhelliferce)  of  the  Archichlamydeae,  which  may 
be  said  to  extend  from  Peppers  to  Umbellifers.  The  Le- 
gumes adopt  zygomorphy,  but  remain  hypogynous  ;  and  in 
some  of  the  Eoses  epigyny  appears ;  but  the  Umbellifers 
with  their  fifteen  hundred  species  are  all  distinctly  epigy- 


FiG.  252.  The  common  carrot  {Daucus  Carota):  A,  branch  bearing  the  compound 
umbels;  B,  a  single  epigynous  flower,  showing  inferior  ovary,  five  spreading 
petals,  five  stamens  alternating  with  the  petals,  and  the  two  styles  of  the  bicarpel- 
lary  pistil;  C,  section  of  flower,  showing  relation  of  parts,  and  also  the  minute 
sepals  near  the  top  of  the  ovary  and  just  beneath  the  other  parts. —After  Warming. 


nous  (Fig.  252,  B,  C),  being  one  of  the  very  few  epigy- 
nous families  among  the  Archichlamydege.  In  addition 
to  epigyny,  the  cyclic  arrangement  and  definite  Dicotyl 
number  is  established,  there  being  five  sepals,  five  petals, 
five  stamens,  and  two  carpels,  the  highest  known  floral 


MONOCOTYLEDONS   AND   DICOTYLEDONS 


267 


formula,  and  one  that  appears  among  the  highest  Sym- 
petalae. 

The  name  of  the  family  is  suggested  by  the  character- 
istic inflorescence,  which  is  also  of  advanced  type.     The 
flowers    are    reduced    in 
size  and  massed  in  flat-        J)"^^f^i^>     ^So 
topped  clusters  called    --'f5,*?=i-A-£.-,T-«rj.?.=?^i'<:? 

nmbels  (Figs.  252,  A,  253). 
The  branches  of  the  clus- 
ter arise  in  cycles  from 
the  axis  like  the  braces 
of  an  umbrella.  As  a  re- 
sult of  the  close  approxi- 
mation of  the  flowers  the 
sepals  are  much  reduced 
in  size  and  often  obsolete 
(Fig.  252,  C). 

The  Umbellifers  are 
mainly  perennial  herbs  of 
the  north  temperate  re- 
gions, forming  a  very  dis- 
tinct family,  and  contain- 
ing the  following  familiar 
forms :  carrot  {Daucus) 
(Fig.  252),  parsnip  {Pasti- 
naca),  hemlock  {Conium) 
(Fig.  253),  pepper-and- 
salt  {Erigenin),  caraway 
{Carum),  fennel  {Fcenic- 
iihtm),  coriander  {Cori- 
andrum),  celery  {xipi- 
um),  parsley  {Petroseli- 
num),  etc.  Allied  to  the 
Umbellifers  are  the  Ara- 
lias  (Araliacece),  and  the 
Dogwoods  {Cornacew). 


Fig.  253.  Hemlock  (Coniuni),  an  Umbellifer, 
showing  the  umbels,  with  the  principal 
rays  rising  from  a  cycle  of  bracts  (i/iro- 
lucre),  and  each  bearing  at  its  summit  a 
secondary  umbel  with  its  cycle  of  second- 
ary bracts  (involucel). — After  Schimpeb. 


268 


PLANT   STRUCTUKES 


SympetalcB 


143.  Introductory. — These  are  the  highest  and  the  most 
recent  Dicotyledons.  While  they  contain  numerous  shrubs 
and  trees  in  the  tropics,  they  are  by  no  means  such  a  shrub 
and  tree  group  in  the  temperate  regions  as  are  the  Archi- 
chlamydese.  The  flowers  are  constantly  cyclic,  the  num- 
ber five  or  four  is  established,  and  the  corolla  is  sympeta- 
lous, the  stamens  usually  being  borne  upon  its  tube  (Figs. 
208,  209,  212). 

There  are  two  well-defined  groups  of  Sympetalae,  distin- 
guished from  one  another  by  the  number  of  cycles  and  the 
number  of  carpels  in  the  flower.  The  group  containing 
the  lower  forms  is  pentacyclic,  meaning  "  cycles  five,"  there 
being  two  sets  of  stamens.  In  it  also  there  are  five  carpels, 
the  floral  formula  being,  Sepals  5,  Petals  5,  Stamens  5  +  5, 
Carpels  5.  As  the  carpels  are  the  same  in  number  as  the 
other  parts,  the  flowers  are  called  isocarpic,  meaning  "  car- 
pels same."  The  group  is  named  either  Pentacyclm  or  Iso- 
carpce,  and  contains  about  ten  families  and  4,000  species. 

The  higher  groups,  containing  about  forty  families  and 
36,000  species,  is  tetracijclic,  meaning  "  cycles  four,"  and 
anisocarpic,  meaning  *'  carpels  not  the  same,"  the  floral 
formula  being.  Sepals  5,  Petals  5,  Stamens  5,  Carpels  2. 
The  group  name,  therefore,  is  Tetracydm  or  Anisocarpoi. 

144.  Heaths. — The  Heath  family  (Ericacece)  and  its  allies 
represent  about  two  thousand  species.  They  are  mostly 
shrubs,  sometimes  trailing,  and  are  displayed  chiefly  in 
temperate  and  arctic  or  alpine  regions,  in  cold  and  damp 
or  dry  places,  often  being  prominent  vegetation  in  bogs 
and  heaths,  to  which  latter  they  give  name  (Fig.  254).  The 
flowers  are  pentacyclic  and  isocarpic,  as  well  as  mostly  hyp- 
ogynous  and  actinomorphic.  It  is  interesting  to  note  that 
some  forms  are  not  sympetalous,  the  petals  being  distinct, 
showing  a  close  relationship  to  the  Archichlamydese.  One 
of  the  marked  characteristics  of  the  group  is  the  dehiscence 


MONOCOTYLEDONS  AND  DICOTYLEDONS 


269 


of  the  pollen-sacs  by  terminal  pores,  which  are  often  pro- 
longed into  tubes  (Fig.  255). 


Fig.  254.  Characteristic  heath  plants:  ,4,  B,  (U  Lyonia.  showing  sympetalous  flowers 
and  single  style  from  the  lobed  syncarpons  ovary;  Z>,  two  forms  of  Casnojie, 
showing  trailing  habit,  small  overlapping  leaves,  and  sympetalous  flowers,  but  in 
the  smaller  form  the  petals  are  almost  distinct.— After  Drudb. 


Common  representatives  of  the  family  are  as  follows  : 
huckleberry  (Gaijlussacia),  cranberry  and  blueberry  (  Vac- 
cinium),  bearberry  (Arcfostaphylos),  trailing  arbutus  [Upi- 


270 


PLANT   STRUCTURES 


gcea),  wintergreen  (GauUheria),  heather  {Calluna),  moun- 
tain laurel  {Kalmia),  Azalea,  Rhododefidron  (Fig.  250), 
Indian  pipe  {Monotropa),  etc. 


Fig.  255.  Flowers  of  heath  plants  (Erica),  showing  compktc  flowers  (4),  the  sta- 
mens wlih  "two-horned"  anthers  which  discharge  pollen  through  terminal  pores, 
and  the  lobed  syncarpous  ovary  with  single  style  and  prominent  terminal  stigma 
(B,  C,  i>).— After  Drude. 


145.  Convolvulus  forms. — The  well-known  morning-glory 
{Ipomcea)  (Fig.  209)  may  be  taken  as  a  type  of  the  Convol- 


MONUCOTYLEDONS   AND    DICOT  i'LEDONS 


271 


vulus  family  {Cunvohmlacece).  Allied  with  it  are  Poleino- 
nium  and  Phlox  (Fig.  210,  b)  {Polemoniacece),  the  gentians 
(Gentianacece),  and  the  dog-banes  {Apocijnacem)  (Fig.  257). 
It  is  here  that  the  regular  sympetalous  flower  reaches  its 
highest  expression  in  the  form  of  conspicuous  tubes,  f un- 


FiG.  256.    A  cluster  of  Rhododendron  flowers.— After  IIooker. 


nels  (Fig.  258),  trumpets,  etc.  The  flowers  are  tetracyclic 
and  anisocarpic,  besides  being  hypogynous  and  actinomor- 
phic.  These  regular  tubular  forms  represent  about  five 
thousand  species,  and  contain  many  of  the  best-known 
flowers. 


272 


PLANT  STRUCTURES 


146.  Labiates. — This  great  family  (LaMatce)  and  its  alli- 
ances represent  more  than  ten  thousand  species.  The  con- 
spicuous feature  is  the 
zygomorjihic  flower,  dif- 
fering in  this  regard  from 
the  Convolvulus  forms, 
which  they  resemble  in 
being  tetracyclic  and  ani- 
socarjiic,  as  well  as  hypogy- 
nous.  The  irregularity 
consists  in  organizing  the 
mouth  of  the  sympetalous 
corolla  into  two  "lips," 
resulting  in  the  labiate  or 


Fig.  2b7.    A  comuiou  du^hauc  X^-ipoci/nuin). —From  "Field,  Forest,  aud  Wayside 

Flowers." 


Fig.  258.     The  hedge  bindweed  { Convulcuius).  showing  the  twining  habit  and  the  con- 
spicuous funnelform  corollas. — From  "  Field,  Forest,  and  Wayside  Flowers." 


274 


PLANT   STKUCTUEES 


MlaUate  structure  (Fig.  210,  c,  d,  e),  and  suggesting  the 
name  of  the  dominant  family.  The  upper  lip  usually  con- 
tains two  petals,  and  the  lower  three  ;  the  two  lips  are  some- 
times widely  separated,  and  sometimes  in  close  contact,  and 
differ  widely  in  relative  prominence. 

Associated  Avith  zygomorphy  in  this  group  is  a  frequent 
reduction  in  the  number  of  stamens,  which  are  often  four 
(Fig.  212)  or  two.  The  whole  structure  is  highly  special- 
ized for  the  visits  of  insects,  and  this  great  zygomorphic 
alliance  holds  the  same 
relative  position  among 
Sympetalae  as  is  held 
by  the  zygomorphic  Le- 
gumes among  Archi- 
chlamydeae. 

In  the  mint  family, 
as  the  Labiates  are  often 
called,  there  are  about 
two  thousand  seven  hun- 
dred species,  including 
mint  {Mentha)  (Fig. 
213),  dittany  {Cunila), 
hyssop  {Hyssopus),  mar- 
joram    {Origanu  m ) , 


Fig.  259.  Flowers  of  dead  nettle  (Xrt- 
miiim) :  A,  entire  bilabiate  flower  ; 
B,  section  of  flower,  showing  rela- 
tion of  parts.— After  Warming. 


Fig.  260.  A  labiate  plant  (Teucrium).  show- 
ing branch  with  flower  clusters  (.-1),  and 
side  view  of  a  few  flowers  {B),  showing 
their  bilabiate  character.— After  Briquet. 


MONOCOTYLEDONS   AND   DICOTYLEDONS  275 

thyme  {Thymus),  balm  {Melissa),  sage  {Salvia),  catnip 
{Nepeta),  skullcap  {Sctitellaria) ,  horehound  {Marruhium), 
iSvender  {Lavandula),  rosemary  {Rosmarinus),  dead  nettle 
{Lamium)  (Fig.  259),  Teucriu?n  (Figs.  213,  260),  etc.,  a 
remarkable  series  of  aromatic  forms. 

Allied  is  the  Nightshade  family  {Solanacew),  with  fif- 
teen hundred  species,  containing  such  common  forms  as 
the  nightshades  and  potato  {Solanu/n),  tomato  {Lycoper- 
sicum),  tobacco  {Nicotiana)  (Fig.  208),  etc.,  in  which  the 
corolla  is  actinomorphic  or  nearly  so  ;  also  the  great  Fig- 
wort  family  {ScrophulariacecB) ,  with  two  thousand  species, 
represented  by  mullein  (  Verhascum),  snapdragon  {Antir- 
rhinum) (Fig.  210,  e),  toad-flax  {Linaria)  (Fig.  210,  c?), 
Pentstemo7i,  speedwell  ( Veronica),  Gerardia,  painted  cup 
{Castilleia),  etc.;  also  the  Verbena  family  {Verbenacew), 
with  over  seven  hundred  species ;  and  the  two  hundred 
plantains  {Planfaginacece),  etc. 

147.  Composites. — This  greatest  and  ranking  family 
( Co7nposit(e)  of  Angiosperms  is  estimated  to  contain  at  least 
twelve  thousand  species,  containing  more  than  one  seventh 
of  all  known  Dicotyledons  and  more  than  one  tenth  of  all 
Seed-plants.  Not  only  is  it  the  greatest  family,  but  it  is 
the  youngest.  Composites  are  distributed  everywhere,  but 
are  most  numerous  in  temperate  regions,  and  are  mostly 
herbs. 

The  name  of  the  family  suggests  the  most  conspicuous 
feature — namely,  the  remarkably  complete  organization  of 
the  numerous  small  flowers  into  a  compact  head  which 
resembles  a  single  flower,  formerly  called  a  "compound 
flower."  Taking  the  head  of  an  Arnica  as  a  type  (Fig. 
261),  the  outermost  set  of  organs  consists  of  more  or  less 
leaf-like  bracts  or  scales  {involucre),  which  resemble  sepals  ; 
within  these  is  a  circle  of  flowers  with  conspicuous  yellow 
corollas  {rays),  which  are  zygomorphic,  being  split  above 
the  tubular  base  and  flattened  into  a  strap-shaped  body, 
and  much  resembling  petals  (Fig.  261,  A,  D) ;  within  the 


Fig.  261.  Flowers  of  Arnica:  A,  lower  part  of  .stem,  and  upper  part  bearing  a 
head,  in  which  are  seen  the  conspicuous  rays  and  the  disk;  D,  single  ray  flower, 
showing  the  corolla,  tubular  at  base  and  strap-shaped  above,  the  two-parted  style, 
the  tuft  of  pappus  hairs,  and  the  inferior  ovary  which  develops  into  a  seed-like 
fruit  (akene);  E,  single  disk  flower,  showing  tubular  corolla  with  spreading  limb, 
the  two-parted  style  emerging  from  the  top  of  the  stamen  tube,  the  prominent 
pappus,  and  the  inferior  ovary  or  akene;   C,  a  single  stamen.— After  Hoffman. 

276 


MONOCOTYLEDONS  AND  DICOTYLEDONS      277 

ray-flowers  is  the  broad  expanse  supplied  by  a  very  much 
broadened  axis,  and  known  as  the  dish  (Fig.  261,  A),  which 
is  closely  packed  with  very  numerous  small  and  regular 
tubular  flowers,  known  as  disk-jioivers  (Fig.  261,  e). 


Fig.  262.  The  common  dandelion  (T'araa'aCTim):  i,  two  flower  stalks;  in  one  the  head 
is  closed,  showing  the  double  involucre,  the  inner  erect,  the  outer  reflexed,  in  the 
other  the  head  open,  showing  that  all  the  flowers  are  strap-shaped;  2,  a  single 
flower  showing  inferior  ovarj'.  pappus,  corolla,  stamen  tube,  and  two-parted  style; 
3,  a  mature  akene;  U,  a  head  from  which  all  but  one  of  the  akenes  have  been  re- 
moved, showing  the  pitted  receptacle  and  the  prominent  pappus  beak.— After 
Strasburger. 

The  division  of  labor  among  the  flowers  of  a  single  head 
is  plainly  marked,  and  sometimes  it  becomes  quite  com- 
plex.    The  closely  packed  flowers  have  resulted  in  modify- 
ing the  sepals  extremely.     Sometimes  they  disappear  en- 
3G 


278 


PLANT   STRUCTURES 


tirely ;  sometimes  t^iey  become  a  tuft  of  delicate  hairs,  as 
in  Arnica  (Fig.  261,  D,  E),  thistle  {Cnictis),  and  dandelion 
{Taraxacum)  (Fig.  263),  surmounting  the  seed-like  akene 
and  aiding  in  its  transportation  through  the  air  ;  sometimes 
they  are  converted  into  two  or  more  tooth-like  and  often 


Fig.  263.  Flowers  of  dandelion,  showing  action  of  style  in  removini;  jxillen  from  the 
stamen  tube:  ;,  style  having  elongated  through  the  tube  and  carrying  pollen;  2, 
style  branches  beginning  to  recurve;  3,  style  branches  completely  recurved.^ 
From  "  Field,  Forest,  and  Wayside  Flowers." 


barbed  processes  arising  from  the  akene,  as  in  tickseed 
(Coreopsis)  and  beggar-ticks  (Fig.  188)  or  Spanish  needles 
(Bidens),  to  lay  hold  of  passing  animals  ;  sometimes  they 
become  beautifully  plumose  bristles,  as  in  the  blazing  star 
(Liatris)  ;  sometimes  they  simply  form  a  more  or  less  con- 
spicuous cup  or  set  of  scales  crowning  the  akene.  In  all 
of  these  modifications  the  calyx  is  called  pappus. 

The  stamens  within  the  corolla  are  organized  into  a 
tube  by  their  coalescent  anthers  (Fig.  263),  and  discharge 
their  pollen  within,  which  is  carried  to  the  surface  of  the 


MONOCOTYLEDONS    AND   DICOTYLEDONS  270 

head  and  exposed  by  the  swab-like  rising  of  the  style  (Fig. 
263).  The  head  is  thus  smeared  with  pollen,  and  visiting 
insects  can  not  fail  to  distribute  it  over  the  head  or  carry 
it  to  some  other  head. 

In  the  dandelion  and  its  allies  the  flowers  of  the  disk 
are  like  the  ray-flowers,  the  corolla  being  zygomorphic  and 
strap-shaped  (Figs.  263,  363). 

The  combination  of  characters  is  sympetalous,  tetracyc- 
lic, and  anisocarpic  flowers,  which  are  epigynous  and  often 
zygomorphic,  with  stamens  organized  into  a  tube  and  calyx 
modified  into  a  pappus,  and  numerous  flowers  organized 
into  a  compact  involucrate  head  in  which  there  is  more  or 
less  division  of  labor.  There  is  no  group  of  plants  that 
shows  such  high  organization,  and  the  Compositae  seem  to 
deserve  the  distinction  of  the  highest  family  of  the  plant 
kingdom. 

The  well-known  forms  are  too  numerous  to  mention, 
but  among  them,  in  addition  to  those  already  mentioned, 
there  are  iron-weed  ( Verno7iia),  Aster,  daisy  {Bellis), 
goldenrod  {Soli dago),  rosin-weed  and  compass-plant  [Silph- 
ium),  sunflower  {Helianthus),  Chrysatithefnum.,  ragweed 
{Ambrosia),  cocklebur  {Xanfhiu?n) ,  ox-eye  daisy  {Leucaii- 
themum),  tansy  {Tanaceium),  wormwood  and  sage-brush 
{Artemisia),  lettuce  {Laduca),  etc. 


CHAPTEE   XV 

DIFFERENTIATION  OF  TISSUES 

148.  Introductory. — Among  the  simplest  Tliallophytes 
the  cells  forming  the  body  are  practically  all  alike,  both  as 
to  form  and  work.  What  one  cell  does  all  do,  and  there 
is  very  little  dependence  of  cells  upon  one  another.  As 
plant  bodies  become  larger  this  condition  of  things  can  not 
continue,  as  all  of  the  cells  can  not  be  put  into  the  same 
relations.  In  such  a  body  certain  cells  can  be  related  to 
the  external  food  supply  only  through  other  cells,  and  the 
body  becomes  differentiated.  In  fact,  the  relating  of  cells 
to  one  another  and  to  the  external  food-supply  makes  large 
bodies  possible. 

The  first  differentiation  of  the  plant  body  is  that  which 
separates  nutritive  cells  from  reproductive  cells,  and  this  is 
accomplished  quite  completely  among  the  Thallophytes. 
The  differentiation  of  the  tissues  of  the  nutritive  body, 
however,  is  that  which  specially  concerns  us  in  this  chapter. 

A  tissue  is  an  aggregation  of  similar  cells  doing  similar 
work.  Among  the  Thallophytes  the  nutritive  body  is  prac- 
tically one  tissue,  although  in  some  of  the  larger  Thallo- 
phytes the  outer  and  the  inner  cells  differ  somewhat.  This 
primitive  tissue,  composed  of  cells  with  thin  walls  and  ac- 
tive protoplasm,  and  to  be  regarded  as  the  parent  tissue,  is 
called  parencliyma. 

Among  the  Bryophytes,  in  the  leafy  gametophore  and 

in  the  sporogonium,  there  is  often  developed  considerable 

dissimilarity  among  the  cells  forming  the  nutritive  body, 

but  the  cells  may  all  still  be  regarded  as  parenchyma.     It 

280 


DIFFERENTIATION   OF  TISSUES 


281 


is  in  the  sporophyte  of  the  Pteridophytes  and  Spermato- 
phytes  that  this  differentiation  of  tissues  becomes  extreme, 
and  tissues  are  organized  which  differ  decidedly  from 
parenchyma.  This  differentiation  means  division  of  labor, 
and  the  more  highly  organized  the  body  the  more  tissues 
there  are. 

All  the  other  tissues  are  derived  from  parenchyma,  and 
as  the  work  of  nutrition  and  of  reproduction  is  ahvays 
retained  by  the  parenchyma  cells,  the  derived  tissues  are 
for  mechanical  rather 
than  for  vital  purposes. 
There  is  a  long  list  of 
these  derived  and  me- 
chanical t'  ^ues,  some  of 
them  being  of  general 
occurrence,  and  others 
more  restricted,  and 
there  is  every  gradation 
between  them  and  the 
parenchyma  from  which 
they  have  come.  We 
shall  note  only  a  few  which  are  distinctly  differentiated 
and  which  are  common  to  all  vascular  plants. 

149.  Parenchyma. — The  parenchyma  of  the  vascular  plants 
is  typically  made  up  of  cells  which  have  thin  walls  and  whose 
three  dimensions  are  approximately  equal  (Figs.  26-1,  265), 
though  sometimes  they  are  elongated.  Until  abandoned, 
such  cells  contain  very  active  protoplasm,  and  it  is  in  them 
that  nutritive  work  and  cell  division  are  carried  on.  So 
long  as  these  cells  retain  the  power  of  cell  division  the 
tissue  is  called  meristem,  or  it  is  said  to  be  mcristematic, 
from  a  Greek  word  meaning  "to  divide."'  When  the  cells 
stop  dividing,  the  tissue  is  said  to  be  permanent.  The 
growing  points  of  organs,  as  stems,  roots,  and  leaves,  are 
composed  of  parenchyma  which  is  mcristematic  (Figs.  266, 
274),  and  meristem  occurs  wherever  growth  is  going  on. 


Pig.  264.  Parenchyma  and  sclerenchyma  from 
the  stem  of  Fteris,  in  cross-section.— Cham- 
berlain. 


282 


PLANT   STKUCTUEES 


150.  Mestome  and  stereome. — When  the  plant  body  be- 
comes complex  a  conductive  system  is  necessary,  so  that 
the  different  regions  of  the  body  may  be  put  into  communi- 
cation. The  material  absorbed 
by  the  roots  must  be  carried  to 
the  leaves,  and  the  food  manu- 
factured in  the  leaves  must 
be  carried  to  regions  of  growth 
and  storage.  This'  business  of 
transportation  is  provided  for 
by  the  specially  organized  ves- 
sels referred  to  in  preceding 
chapters,  and  all  conducting  tis- 
sue, of  whatever  kind,  is  spoken 
of  collectively  as  mestorne. 

If  a  complex  body  is  to  main- 
tain its  form,  and  especially  if 
it  is  to  stand  upright  and  be- 
come large,  it  must  develop 
structures  rigid  enough  to  fur- 
nish mechanical  support.  All 
the  tissues  which  serve  this  pur- 
pose are  collectively  known  as 
stereome. 

The     sporophyte     body     of 

Pteridophytes    and    Spermato- 

phytes,     therefore,     is     mostly 

made   up   of   living  and  working  parenchyma,  which  is 

traversed  by  mechanical  mestome  and  stereome. 

151.  Dicotyl  and  Conifer  stems. — The  stems  of  these  two 
groups  are  so  nearly  alike  in  general  plan  that  they  may 
be  considered  together.  In  fact,  the  resemblances  were 
once  thouglit  to  be  so  important  that  these  two  groups 
were  put  together  and  kept  distinct  from  Monocotyledons  ; 
but  this  was  before  the  gametophyte  structures  were 
known  to  bear  very  different  testimony. 


\ 

Fig.  265.  Same  tissues  as  in  pre- 
ceding figure,  in  longitudinal  sec- 
tion, the  parenchyma  showing 
nuclei.— Chamberlain. 


DIFFEKENTIATION   OF   TISSUES 


283 


At  the  apex  of  the  growing  stem  there  is  a  group  of 
active  meristem  cells,  from  which  all  the  tissues  are  de- 
rived (Fig.  266).  This  group  is  known  as  the  apical  group. 
Below  the  apical  group  the  tissues  and  regions  of  the  stem 
begin  to  appear,  and  still  farther  down  they  become  dis- 
tinctly differentiated,  passing  into  permanent  tissue,  the 
apical  group  by  its 
divisions  continually 
adding  to  them  and 
increasing  the  stem 
in  length. 

Just  behind  the 
apical  group,  the 
cells  begin  to  give  the 
appearance  of  being 
organized  into  three 
great  embryonic  re- 
gions, the  cells  still 
remaining  meristem- 
atic  (Fig.  266).  At 
the  surface  there  is  a 
single  layer  of  cells 
distinct    from    those 

within,  known  as  the  dermatogen^  or  "  skin-producer,"  as 
farther  down,  where  it  becomes  permanent  tissue,  it  is  the 
epidermis.  In  the  center  of  ^the  embryonic  region  there 
is  organized  a  solid  cylinder  of  cells,  distinct  from  those 
around  it,  and  called  the  plerome,  meaning  "that  which 
fills  up."  Farther  down,  where  the  plerome  passes  into 
permanent  tissue,  it  is  called  the  central  cylinder  or  stele 
("column").  Between  the  plerome  and  dermatogen  is 
a  tissue  region  called  the  perihlem,  meaning  "that  which 
is  put  around,"  and  when  it  becomes  permanent  tissue  it 
is  called  the  cortex,  meaning  "bark  "  or  "rind," 

Putting  these  facts  together,  the  general  statement  is 
that  at  the  apex  there  is  the  apical  group  of  meristem  cells  ; 


Fig.  266.  Section  through  growing  point  of  stem  of 
Hippuris  :  below  the  growing  point,  composed 
of  a  uniform  meristem  tissue,  the  three  embry- 
onic regions  are  outlined,  showing  the  dermato- 
gen (d,  d),  the  central  plerome  (p.p).  and  be- 
tween them  the  periblem. — After  De  Bart. 


284 


PLANT   STEUCTUKES 


below  them  are  the  three  embryonic  regions,  dermatogen, 
periblem,  and  plerome ;  and  farther  below  these  three 
regions  pass  into  permanent  tissue,  organizing  the  epider- 
mis, cortex,  and  stele.  The  three  embryonic  regions  are 
usually  not  so  distinct  in  the  Conifer  stem  as  in  the  Dico- 
tyl  stem,  but  both  stems  have  epidermis,  cortex,  and  stele. 
Epidermis. — The  epidermis  is  a  protective  layer,  whose 
cells  do  not  become  so  much  modified  but  that  they  may 
be  regarded  as  parenchyma.  It  gives  rise  also  to  super- 
ficial parts,  as  hairs,  etc.  In  the  case  of  trees,  the  epidermis 
does  not  usually  keep  up  with  the  increasing  diameter,  and 
disappears.  This  puts  the  work  of  protection  upon  the 
cortex,  which  organizes  a  superficial  tissue  called  cork,  a 
prominent  part  of  the  structure  known  as  hai'lc. 

Cortex. — The  cortex  is  characterized  by  containing 
much  active  parenchyma,  or  primitive  tissue,  being  the 
chief  seat  of  the  life  activities  of  the  stem.  Its  superficial 
cells,  at  least,  contain  chlorophyll  and  do  chlorophyll  work, 
while  its  deeper  cells  are  usually  temporary  storage  places 

for  food.  The  cortex  is  also  char- 
acterized by  the  development  of 
stereome,  or  rigid  tissues  for  me- 
chanical support.  The  stereome 
may  brace  the  epidermis,  forming 
the  hypodermis ;  or  it  may  form 
bands  and  strands  within  the  cor- 
tex ;  in  fact,  its  amount  and  ar- 
rangement differ  widely  in  differ- 
ent plants. 

The  two  principal  stereome  tis- 
sues are  collenchynia  and  scleren- 
chyma,  meaning  "sheath-tissue" 
and  "  hard-tissue "  respectively. 
In  collenchyma  the  cells  are  thick- 
ened at  the  angles  and  have  very  elastic  walls  (Fig.  267), 
making  the  tissue  well  adapted  for  parts  which  are  growing 


Fig.  267.  Some  collenchyma 
cells  from  the  stem  of  a  com- 
mon dock  iRuinex),  showing 
the  cells  thickened  at  the 
angles.— Chamberlain. 


DIFFERENTIATION   OF  TISSUES 


285 


in  length.  The  chief  mechanical  tissue  for  parts  which 
have  stopped  growing  in  length  is  sclerenchyma  (Figs.  264, 
265).  The  cells  are  thick-walled,  and  usually  elongated 
and  with  tapering  ends,  including  the  so-called  "fihers." 


Fig.  268.  Sections  through  an  open  collateral  vascular  bundle  from  a  sunflower  stem; 
A,  cross-section;  B.  longittulinal  section:  the  letters  in  both  referring  to  the  same 
structures;  3/,  pith;  X  xylom.  containing  spiral  {c, .«')  and  pitted  (t.  I')  vessels; 
C,  cambium;  P,  phloem,  containing  sieve  vessels  (sb)\  b,  a  mass  of  bast  fibers  or 
sclerenchyma;  ic,  pith  rays  between  the  bundles;  e,  the  bundle  sheath;  R,  cor- 
tex.—After  Vines. 

Stele. — The  characteristic  feature  of  the  stele  or  central 
cylinder  is  the  development  of  the  mestome  or  vascular 


286 


PLANT   STRUCTURES 


tissues,  of  which  there  are  two  prominent  kinds.  The 
tracheary  vessels  are  for  water  conduction,  and  are  cells 
with  heavy  walls  and  usually  large  diameter  (Fig.  268). 
The  thickening  of  the  walls  is  not  uniform,  giving  them  a 
very  characteristic  appearance,  the  thickening  taking  the 
form  of  spiral  bands,  rings,  or  reticulations  (Fig.  308,  B). 
Often  the  reticulation  has  such  close  meshes  that  the  cell 
wall  has  the  appearance  of  being  covered  with  thin  spots, 
and  such  cells  are  called  "  pitted  vessels."  The  vessels  with 
spirals  and  rings  are  usually  much  smaller  in  diameter  than 
the  pitted  ones.  The  true  tracheary  cells  are  more  or  less 
elongated  and  without  tapering  ends,  fitting  end  to  end 
and  forming  a  continuous  longitudinal  series,  suggesting  a 
trachea,  and  hence  the  name.     In  the  Conifers  there  are 

no  true  tracheary  cells,  as  in 
the  Dicotyledons,  except  a  few 
small  spiral  vessels  which  are 
formed  at  first  in  the  young 
stele,  but  the  tracheary  tissue 
is  made  up  of  traclieids,  mean- 
ing "  trachea  -  like,"  differing 
from  trachem  or  true  tracheary 
vessels  in  having  tapering  ends 
and  in  not  forming  a  continu- 
ous series  (Fig.  2(50).  The  walls 
of  these  tracheids  are  "pitted" 
in  a  way  which  is  characteristic 
of  Gymnosperms,  the  "pits" 
appearing  as  two  concentric 
rings,  called  "bordered  pits." 

The  other  prominent  mes- 
tome  tissue  developed  in  the 
stele  is  the  sieve  vessels,  for  the 
conduction  of  organized  food,  chiefly  proteids  (Fig.  2G8). 
Sieve  cells  are  so  named  because  in  their  walls  special  areas 
are  organized  which  are  perforated  like  the  lid  of  a  pepper- 


FiG.  269.  Tracheids  from  wood  of 
pine,  showing  tapering  ends  and 
bordered  pits.— Chamberlain. 


DIFFERENTIATION   OF  TISSUES  287 

box  or  a  "sieve."  These  perforated  areas  are  the  sieve- 
plates,  and  through  them  the  vessels  communicate  with 
one  another  and  with  the  adjacent  tissue. 

The  tracheary  and  sieve  vessels  occur  in  separate 
strands,  the  tracheary  strand  being  called  xylem  ("  wood  "), 
the  sieve  strand  phloem.  ("  bark  ").  A  xylem  and  a  phloem 
strand  are  usually  organized  together  to  form  a  vascular 
hiindle,  and  it  is  these  fiber-like  bundles  which  are  found 
traversing  the  stems  of  all  vascular  plants  and  appearing 
conspicuously  as  the  veins  of  leaves.  Among  the  Dicotyls 
and  Conifers  the  vascular  bundles  appear  in  the  stele  in 
such  a  way  as  to  outline  a  hollow  cylinder  (Fig.  216),  the 
xylem  of  each  bundle  being  toward  the  center,  the  phloem 
toward  the  circumference  of  the  stem.  The  undifEerenti- 
ated  parenchyma  of  the  stele  which  the  vascular  cylinder 
incloses  is  called  the  pith.  In  older  parts  of  the  stem  the 
pith  is  often  abandoned  by  the  activities  of  the  plant,  and 
either  remains  as  a  dead  spongy  tissue,  or  disappears  en- 
tirely, leaving  a  hollow  stem.  Between  the  bundles  form- 
ing the  vascular  cylinder  there  is  also  undifferentiated 
parenchyma,  and  as  it  seems  to  extend  from  the  pith  out 
between  the  bundles  like  "rays  from  the  sun,"  the  rays 
are  called  pitli  rays. 

Such  vascular  bundles  as  described  above,  in  which  the 
xylem  and  phloem  strands  are  "  side-by-side  "  upon  the  same 
radius,  are  called  collateral  (Fig.  270).  One  of  the  pecul- 
iarities of  the  collateral  bundles  of  Dicotyls  and  Conifers, 
however,  is  that  when  the  two  strands  of  each  bundle  are 
organized  some  meristem  is  left  between  them.  This  means 
that  between  the  strands  the  work  of  forming  new  cells  can 
go  on.  Such  bundles  are  said  to  be  open ;  and  the  open 
collateral  bundle  is  characteristic  of  the  stems  of  the  Dico- 
tyls and  Conifers. 

The  meristem  between  the  xylem  and  phloem  of  the 
open  bundle  is  called  cambium  (Figs.  268,  270).  The  cam- 
bium also  extends  across  the  pith  rays  between  the  bundles. 


288 


PLANT   STRUCTURES 


connecting  the  cambium  in  the  bundles,  and  thus  forming 
a  cambium  cylinder,  which  separates  the  xylem  and  phloem 
of  the  vascular  cylinder.     This  cambium  continues  the  f  or- 


FiG.  270.  Cross-section  of  open  collateral  vascular  bundle  from  stem  of  castor-oi! 
plant  (Rlclnus),  showing  pith  cells  (m),  xylem  containing  spiral  {t)  and  pitted  {g) 
vessels,  cambium  of  bundle  (c)  and  of  pith  rays  (cb),  phloem  containing  sieve  ves 
sels  (y\  three  bundles  of  bast  fibers  or  sclerenchyma  (b),  the  bundle  sheath  con' 
taining  starch  grains,  and  outside  of  it  parenchyma  of  the  cortex  (»•).— After  Sachs 

mation  of  xylem  tissue  on  the  one  side  and  phloem  tissue 
on  the  other  in  the  bundles,  and  new  parenchyma  between 
the  bundles,  and  so  the  stem  increases  in  diameter.  If  the 
stem  lives  from  year  to  year  the  addition  made  by  the  cam- 
bium each  season  is  marked  off  from  that  of  the  previous 
season,  giving  rise  to  the  so-called  growth  rings  or  annual 
rings,  so  conspicuous  a  feature  of  the  cross-section  of  tree 


DIFFEKENTIATION   OF  TISSUES  289 

trunks  (Fig.  217).  This  continuous  addition  to  the  vessels 
increases  the  capacity  of  the  stem  for  conduction,  and  per- 
mits the  furtlier  extension  of  branches  and  a  larger  display 
of  leaves. 

The  annual  additions  to  the  xylem  are  added  to  the  in- 
creasing mass  of  wood.  The  older  portions  of  the  xylem 
mass  are  gradually  abandoned  by  the  ascending  water 
C'sap"),  often  change  in  color,  and  form  the  lieart-ivood. 
The  younger  portion,  through  which  the  sap  is  moving,  is 
the  sap-wood.  It  is  evident,  however,  that  the  annual  ad- 
ditions to  the  phloem  are  not  in  a  position  for  permanency. 
The  new  phloem  is  deposited  inside  of  the  old,  and  this,  to- 
gether with  the  new  xylem,  presses  upon  the  old  phloem, 
which  becomes  ruptured  in  various  ways,  and  rapidly  or 
very  gradually  peels  off,  being  constantly  renewed  from 
within.  It  is  the  protecting  layers  of  cork  (see  this  section 
under  Cortex),  the  old  phloem,  and  the  new  phloem  down 
to  the  cambium,  which  constitute  the  so-called  bark  of 
trees,  a  structure  exceedingly  complex  and  extremely  vari- 
able in  different  trees. 

The  stele  also  frequently  develops  stereome  tissue  in  the 
form  of  sclerenchyma.  These  thick-walled  fibers  are  often 
closely  associated  with  one  or  both  of  the  vascular  strands 
of  the  bundles  (Fig.  270),  and  lead  to  the  old  name  Jibro- 
vascular  bundles. 

To  sum  up,  the  stems  of  Dicotyledons  and  Conifers  are 
characterized  by  the  development  of  a  vascular  cylinder,  in 
which  the  bundles  are  collateral  and  open,  permitting 
increase  in  diameter,  extension  of  the  branch  system,  and 
a  continuous  increase  in  leaf  display. 

152.  Monocotyl  steins. — In  the  stems  of  Monocotyledons 
there  is  the  same  apical  development  and  differentiation 
(Fig.  266).  The  characteristic  difference  from  the  Dicotyl 
and  Conifer  type,  just  described,  is  in  connection  with  the 
development  of  the  vascular  bundles  in  the  stele.  Instead 
of  outlining  a  hollow  cylinder,  the  bundles  are  scattered 


290 


PLANT   STRUCTURES 


through  the  stele  (Fig.  214).  This  lack  of  regularity  would 
interfere  with  the  organization  of  a  cambium  cylinder,  and 
we  find  the  bundles  collateral  but  closed — that  is,  with  no 
meristem  left  between  the  xylem  and  phloem  (Fig.  371). 


Fig.  271.  Cross-section  of  a  closed  collateral  bundle  from  the  stem  of  corn,  showing 
the  xylem  with  annular  (r),  spiral  (s),  and  pitted  {g^  vessels;  the  phloem  contain- 
ing sieve  vessels  (v),  and  separated  from  the  xylem  by  no  intervening  cambium; 
both  xylem  and  phloem  surrounded  by  a  mass  of  sclerenchyma  (fibers);  and  in- 
vesting vessels  and  fibers  the  parenchyma  (;>)  of  the  pith-like  tissue  through 
which  the  bundles  are  distributed.— After  Sachs. 


This  lack  of  cambium  means  that  stems  living  for  sev- 
eral years  do  not  increase  in  diameter,  but  become  columnar 


DIFFERENTIATION   OF  TISSUES  291 

shafts,  as  in  the  palm,  rather  than  much  elongated  cones. 
It  also  means  lack  of  ability  to  develop  an  extending  branch 
system  or  to  display  more  numerous  leaves  each  year.  The 
palm  may  be  taken  as  a  typical  result  of  such  a  structure, 
with  its  columnar  and  unbranched  trunk,  and  its  foliage 
crown  containing  about  the  same  number  of  leaves  each  year. 

The  lack  of  regular  arrangement  of  the  bundles  also 
prevents  the  outlining  of  a  pith  region  or  the  organization 
of  definite  pith  rays.  The  failure  to  increase  in  diameter 
also  precludes  the  necessity  of  bark,  with  its  protective  cork 
constantly  renewed,  and  its  sloughing-off  phloem. 

To  sum  up,  the  stems  of  the  Monocotyledons  are 
characterized  by  the  vascular  bundles  not  developing  a 
cylinder  or  any  regular  arrangement,  and  by  collateral  and 
closed  bundles,  which  do  not  permit  increase  in  diameter, 
or  a  branch  system,  or  increase  in  leaf  display. 

153.  Pteridophyte  steins. — The  stems  of  Pteridophytes 
are  quite  different  from  those  of  Spermatophytes.  While 
the  large  Club -mosses  {Lyco- 
2)odium)  and  Jsoetes  usually 
have  an  apical  group  of  meris- 
tem  cells,  as  among  the  Seed- 
plants,  the  smaller  Club-mosses 
{Selaginella),  Ferns,  and  Horse- 
tails usually  have  a  single  api- 
cal cell,  whose  divisions  give 

i        n  j-i,  11     „j!^u^„4-„«.         Fig.  272.   Diagram  of  tissueg  in  cross- 

rise  to  all  the  cells  oi  the  stem.  ^.      ,  ",       ,    ,     ,  „,   . , 

section  of  stem  of  a  icmiPteris), 

Generally  also  a  dermatogen  is  showing  two  masses  of  scieren- 
not    organized,    and    in    such        '^'jy^  '*'^>'  ^«'"7^°  and  about 

^         _  _  _  which     are    vascular    bundles.  — 

cases  there  is  no  true  epidermis,  chamberlain. 
the  cortex  developing  the  ex- 
ternal protective  tissue.  In  the  cortex  there  is  usually  an 
extensive  development  of  stereome,  in  the  form  of  scleren- 
chyma  (Fig.  272),  the  stele  furnishing  little  or  none,  and 
the  vascular  bundles  not  adding  much  to  the  rigidity,  as 
they  do  in  the  Seed-plants. 


292  PLANT   STRUCTUEES 

In  Equisetum  and  Isoefes  the  vascular  bundles  may  be 
said  to  be  collateral,  as  in  the  Seed-plants,  but  the  charac- 
teristic Pteridophyte  type  is  very  different.  In  fact,  the 
vascular  masses  can  hardly  be  compared  with  the  bundles 
of  the  Seed-plants,  although  they  are  called  bundles  for 
convenience.  In  the  stele  one  or  more  of  these  bundles 
are  organized  (Fig.  272),  the  tracheary  vessels  (xylem)  being 
in  the  center  and  completely  invested  by  the  sieve  vessels 


Fig.  273.  Cross-section  of  concentric  vascular  bundle  of  a  fern  (Pleris):  the  single 
row  of  shaded  cells  investing  the  others  is  the  bundle  sheath;  the  large  and  heavy- 
walled  cells  within  constitute  the  xylem;  and  between  the  xylem  and  the  bundle 
shealh  is  the  phloem. — Chamberlain. 

(phloem).  This  is  called  the  concentric  bundle  (Fig.  273), 
as  distinguished  from  the  collateral  bundles  of  Seed-plants, 
and  is  characteristic  of  Pteridophyte  stems. 


DIFFERENTIATION   OF   TISSUES 


293 


154.  Roots. — True  roots  appear  only  in  connection  with 
the  vascular  plants  (Pterido2)hytes  and  Spermatophytes)  ; 


P 


P 


Pig.  274.  Section  through  root- 
tip  of  P/eris:  the  cell  with 
a  nucleus  is  the  single  apical 
cell,  which  in  front  has  cut 
off  cells  which  organize  the 

root-cap. — CUAMBEULAIN. 

and  in  all  of  them  the 
structure  is  essential- 
ly the  same,  and  quite 
d liferent  from  stem 
structure.  A  single 
apical  cell  (in  most 
Pteridophytes)  (Fig. 
274)  or  an  apical 
group  (in  Spermato- 
phytes) usually  gives 
rise  to  the  three  em- 
bryonic regions — der- 
raatogen,  periblem, 
and  plerome  (Fig. 
275).  A  fourth  re- 
gion, however,  pecul- 
iar to  root,  is  usually  added.  The  a,pical  cell  or  group  cuts 
off  a  tissue  in  front  of  itself  (Fig.  274),  known  as  the  cali/p- 
trogen,  or  "  cap  producer,"  for  it  organizes  the  root-cap, 
which  protects  the  delicate  moristem  of  the  growing  })oiiit. 
37 


Fio.  275.  A  longitudinal  section  through  the  root- 
tip  of  spiderwort,  showing  the  plerome  { pl), 
surrounded  by  the  periblem  ( p),  outside  of 
periblem  the  epidermis  (<?)  which  disappears  in 
the  older  parts  of  the  root,  and  the  prominent 
root-cap  (c).— Land. 


294 


PLANT   STKUCTUKES 


Another  striking  feature  is  that  in  the  stele  there  is 
organized  a  single  solid  vascular  cylinder,  forming  a  tough 
central  axis  (Fig.  277),  from  which  the  usually  well-devel- 
oped cortex  can  be  peeled  off  as  a  thick  rind.  In  this  vas- 
cular axis,  which  is  called  "  a  hundle  "  for  convenience  but 
does  not  represent  the  bundle  of  Seed-plant  stems,  the  ar- 
rangement of  the  xylem  and  phloem  is  entirely  unlike  that 


Fig.  276.   Cross-section  of  the  vascular  axis  of  a  root,  showing  radiate  type  of  bundle, 
the  xylem  (p)  and  phloem  (ph)  alternating.— After  Sachs. 

found  in  stems.  The  xylem  is  in  the  center  and  sends  out 
a  few  radiating  arms,  between  which  are  strands  of  phloem, 
forming  the  so-called  radiate  bundle  (Fig.  276).  This 
arrangement  brings  the  tracheary  vessels  (xylem)  to  the 
surface  of  the  bundle  region,  which  is  not  true  of  either 
the  concentric  or  collateral  bundle.  This  seems  to  be  asso- 
ciated with  the  fact  that  the  xylem  is  to  receive  and  conduct 
the  water  absorbed  from  the  soil.  It  should  be  said  that 
this  characteristic  bundle  structure  of  the  root  appears  only 


DIFFERENTIATION    OF   TISSUES 


295 


in  young  and  active  roots.  In  older  ones  certain  secondary 
changes  take  place  which  obscure  the  structure  and  result 
in  a  resemblance  to  the  stem. 

The  origin  of  branches  in 
roots  is  also  peculiar.  In  stems 
branches  originate  at  the  sur- 
face, involving  epidermis,  cor- 
tex, and  vascular  bundles,  such 
an  origin  being  called  exogenous 
("  produced  outside ") ;  but  in 
roots  branches  originate  on 
the  vascular  cylinder,  burrow 
through  the  cortex,  and  emerge 
at  the  surface  (Fig.  277).  If  the 
corl:ex  be  stripped  ofE  from  a 
root  with  branches,  the  branches 
are  left  attached  to  the  woody 
axis,  and  the  cortex  is  found 
pierced  with  holes  made  by  the  burrowing  branches.  Such 
an  origin  is  called  endogenous,  meaning  "  produced  within." 


Fig.  277.  Endogenous  origin  of 
root  branches,  showing  them  (n) 
arising  from  the  central  axis  (/) 
and  breaking  through  the  cortex 
(?•).— After  Vines. 


Pig.  278.  A  section  through  the  leaf  of  lily,  showing  upper  epidermis  (ue),  lower  epi- 
dermis (le)  with  its  stomata  (*0.  mesophyll  (dotted  cells)  composed  of  the  palisade 
region  (p)  and  the  spongy  region  {up)  with  air  spaces  among  the  cells,  and  two 
veins  (»)  cut  across. — From  "  Plant  Relations." 


29r)  PLANT    STKLICTUKKS 

To  sum  up  the  peculiarities  of  the  root,  it  may  be  said 
to  develop  a  root-eap,  to  have  a  solid  vascular  cylinder  in 
v.'hich  the  xylem  and  phloem  are  arranged  to  form  a  bundle 
of  the  radiate  type,  and  to  branch  endogenously. 

155.  Leaves. — Leaves  usually  develop  from  an  apical 
region  in  the  same  general  way  as  do  stems  and  roots, 
modified  by  their  common  dorsiventral  character.  Com- 
paring the  leaf  of  an  ordinary  seed-plant  with  its  stem,  it 
will  be  noted  that  the  three  regions  are  represented  (Fig. 
278):  (1)  the  epidermis;  (2)  the  cortex,  represented  by 
the  meso2ihyll ;  (3)  the  stele,  rejiresented  by  the  veins. 

In  the  case  of  collateral  bundles,  where  in  the  stem  the 
xylem  is  always  toward  the  center  and  the  phloem  is  toward 
the  circumference,  in  the  leaves  the  xylem  is  toward  the 
upper  and  the  phloem  toward  the  lower  surface. 


CHAPTEE   XVI 

PLANT  PHYSIOLOGY 

156.  Introductory. — Plants  may  be  studied  from  several 
points  of  view,  each  of  which  has  resulted  in  a  distinct 
division  of  Botany.  The  study  of  the  forms  of  plants  and 
their  structure  is  Morphology,  and  it  is  this  phase  of  Bot- 
any which  has  been  chiefly  considered  in  the  previous  chap- 
ters. The  study  of  plants  at  work  is  Physiology,  and  as 
structure  is  simply  preparation  for  work,  the  preceding 
chapters  have  contained  some  Physiology,  chiefly  in  refer- 
ence to  nutrition  and  reproduction.  The  study  of  the  clas- 
sification of  plants  is  Taxonomy,  and  in  the  preceding 
pages  the  larger  groups  have  been  outlined.  The  study  of 
plants  as  to  their  external  relations  is  Ecology,  a  subject 
which  will  be  presented  in  the  following  chapter,  and  which 
is  the  chief  subject  of  Plant  Eelations.  The  study  of  the 
diseases  of  plants  and  their  remedies  is  Pathology  ;  their 
study  in  relation  to  the  interests  of  man  is  Economic 
Botany. 

Besides  these  general  subjects,  which  apply  to  all  plants, 
the  different  groups  form  the  subjects  of  special  study.  The 
study  of  the  Morphology,  Physiology,  or  Taxonomy  of  the 
Bacteria  is  Hftcfen'ologi/ ;  of  the  Alg»,  Algology ;  of  the 
Fungi,  Mycologii ;  of  the  Bryophytes,  Bryology ;  of  the 
fossil  plants,  PaJ(Pohof(tny  or  Palceopliytology,  etc. 

In  the  present  chapter  it  is  the  purpose  to  give  a  very 
brief  outline  of  the  great  subject  of  Plant  Physiology,  not 
with  the  expectation  of  presenting  its  facts  adequately,  but 
with  the  hope  that  the  important  field  thus  presented  may 

297 


298  PLANT   STRUCTUKES 

attract  to  further  study.    It  is  merely  the  opening  of  a  door 
to  catch  a  fleeting  glimpse. 

A  common  division  of  the  subject  presents  it  under  five 
heads  :  (1)  Stability  of  form,  (2)  Nutrition,  (3)  Kespira- 
tion,  (4)  Movement,  (5)  Eeproduction. 

STABILITY    OF    FOEM 

157.  Turgidity. — It  is  a  remarkable  fact  that  plants  and 
parts  of  plants  composed  entirely  of  cells  with  very  thin  and 
delicate  walls  are  rigid  enough  to  maintain  their  form. 
It  has  already  been  noted  (see  §  20)  that  such  active  cells 
exert  an  internal  pressure  upon  their  vralls.  This  seems  to 
be  due  to  the  active  absorption  of  liquid,  which  causes  the 
very  elastic  walls  to  stretch,  as  in  the  "blowing  up  "  of  a 
bladder.  In  this  way  each  gorged  and  distended  cell  be- 
comes comparatively  rigid,  and  the  mass  of  cells  retains  its 
form.  It  seems  evident  that  the  active  protoplasm  greedily 
pulls  liquid  through  the  wall  and  does  not  let  it  escape  so 
easily.  If  for  any  reason  the  protoplasm  of  a  gorged  cell 
loses  its  hold  upon  the  contained  liquid  the  cell  collapses. 

158.  Tension  of  tissues. — The  rigidity  which  comes  to 
active  parenchyma  cells  through  their  turgidity  is  increased 
by  the  tensions  developed  by  adjacent  tissues.  For  exam- 
ple, the  internal  and  external  tissues  of  a  stem  are  apt  to 
increase  in  volume  at  different  rates ;  the  faster  will  jjull 
upon  the  slower,  and  the  slower  will  resist,  and  thus  be- 
tween the  two  a  tension  is  developed  which  helps  to  keep 
them  rigid.  This  is  strikingly  shown  by  splitting  a  dande- 
lion stem,  when  the  inner  tissue,  relieved  somewhat  from 
the  resistance  of  the  outer,  elongates  and  causes  the  strip 
to  become  strongly  curved  outward  or  even  coiled.  Experi- 
ments with  strips  from  active  twigs,  including  the  pith, 
will  usually  demonstrate  the  same  curve  outward.  Tension 
of  tissues  is  chiefly  developed,  of  course,  where  elongation 
is  taking  place. 


PLANT  PHYSIOLOGY 


299 


159.  Stereome. — When  growth  is  completed,  cell  walls 
lose  their  elasticity,  turgidity  becomes  less,  and  therefore 
tensions  diminish,  and  rigidity  is  supplied  by  special  ster- 
eome tissues,  chief  among  which  is  sclerenchyma.  An- 
other stereome  tissue  is  collenchyma,  which  on  account  of 
its  elastic  walls  can  be  used  to  supplement  turgidity  and 
tension  where  elongation  is  still  going  on.  For  a  fuller 
account  of  stereome  tissues  see  §  150. 

NUTEITION" 

160.  Food. — Plant  food  must  contain  carbon  (C),  hydro- 
gen (H),  oxygen  (0),  and  nitrogen  (N),  and  also  more 
or  less  of  other  elements,  notably  sulphur,  phosphorus, 
potassium,  calcium,  magnesium,  and  iron.  In  the  case 
of  green  plants  these  elements  are  obtained  from  inor- 
ganic compounds  and  food  is  manufactured  ;  while  plants 
without  chlorophyll  obtain  their  food  already  organized. 
The  sources  of  these  elements  for  green  plants  are  as 
follows  :  Carbon  from  carbon  dioxide  (COg)  of  the  air ; 
hydrogen  and  oxygen  from  water  (HgO) ;  and  nitrogen 
and  the  other  elements  from  their  various  salts  which 
occur  in  the  soil  and  are  dissolved  in  the  water  which 
enters  the  plant. 

All  of  these   substances   must   present  themselves   to 

plants  in  the  form  of  a  gas  or  a  liquid,  as  they  must  pass 

through  cell  walls  ;  and  the  processes  of  absorption  have 

to  do  with  the  taking  in  of  the  gas  carbon  dioxide  and  of 

'  water  in  which  the  necessary  salts  are  dissolved. 

161.  Absorption. — Green  plants  alone  will  be  considered, 
as  the  unusual  methods  of  securing  food  have  been  men- 
tioned in  Chapter  VII.  For  convenience  also,  only  terres- 
trial green  plants  will  be  referred  to,  as  it  is  simple  to 
modify  the  processes  to  the  aquatic  habit,  where  the  sur- 
rounding water  supplies  what  is  obtained  by  land  plants 
from  both  air  and  soil. 


300  PLANT   STRUCTURES 

In  such  plants  the  carbon  dioxide  is  absorbed  directly 
from  the  air  by  the  foliage  leaves,  whose  expanse  of  surface 
is  as  important  for  this  purpose  as  for  exposing  chlorophyll 
"to  light.  When  the  work  of  foliage  leaves  is  mentioned  it 
must  always  be  understood  that  it  applies  as  well  to  any 
green  tissue  displayed  by  the  plant. 

The  water,  with  its  dissolved  salts,  is  absorbed  from  the 
soil  by  the  roots.  Only  the  youngest  parts  of  the  root- 
system  can  absorb,  and  the  absorbing  capacity  of  these 
parts  is  usually  vastly  increased  by  the  development  of 
numerous  root  hairs  just  behind  the  growing  tip  (Fig.  194). 
These  root  hairs  are  ephemeral,  new  ones  being  continu- 
ally put  out  as  the  tip  advances,  and  the  older  ones  disap- 
pearing. They  come  in  very  close  contact  with  the  soil 
particles,  and  "  suck  in  "  the  water  which  invests  each 
particle  as  a  film. 

162.  Transfer  of  water. — The  water  and  its  dissolved  salts 
absorbed  by  the  root-system  must  be  transferred  to  the  foli- 
age leaves,  where  they  are  to  be  used,  along  with  the  carbon 
dioxide,  in  the  manufacture  of  food. 

Having  entered  the  epidermis  of  the  absorbing  rootlets 
the  water  passes  on  to  the  cortex,  and  traversing  it  enters 
the  xylem  system  of  the  central  axis.  In  some  way  this 
transfer  is  accompanied  by  pressure,  known  as  root  pres- 
sure, which  becomes  very  evident  when  an  active  stem  is 
cut  off  near  the  ground.  The  stump  is  said  to  "bleed," 
and  sends  out  water  ("  sap ")  as  if  there  were  a  force 
pump  in  the  root-system.  This  root  pressure  doubtless 
helps  to  lift  the  water  through  the  xylem  of  the  root  into 
the  stem,  and  in  low  plants  may  possibly  be  able  to  send  it 
to  the  leaves,  but  for  most  plants  this  is  not  possible. 

When  the  water  enters  the  xylem  of  the  root  it  is  in  a 
continuous  system  of  vessels  which  extends  through  the 
stem  and  out  into  the  leaves.  The  movement  of  the  ab- 
sorbed water  through  the  xylem  is  called  the  transpiration 
current,  or  very  commonly  the  "ascent  of  sap."     An  ex- 


PLANT   PHYSIOLOGY  301 

periment  demonstrating  this  ascent  of  sap  and  its  route 
through  the  xykmi  will  be  found  described  in  Plant  Rela- 
tions, p.  151.  How  it  is  that  the  transpiration  current 
moves  through  the  xylem  is  not  certainly  known. 

163.  Transpiration. — When  the  water  carrying  dissolved 
salts  reaches  the  mesophyll  cells,  some  of  the  water  and  all 
of  the  salts  are  retained  for  food  manufacture.  However, 
much  more  water  enters  the  leaves  than  is  needed  for  food, 
this  excess  having  been  used  for  carrying  soil  salts.  When 
the  soil  salts  have  reached  their  destination  the  excess  of 
water  is  evaporated  from  the  leaf  surface,  the  process  being 
called  transpiration.  For  an  experiment  demonstrating 
transpiration  see  Plant  Eelafions,  §  26. 

This  transpiration  is  regulated  according  to  the  needs 
of  the  plant.  If  the  water  is  abundant,  transpiration  is 
encouraged ;  if  the  water  supply  is  low,  transpiration  is 
checked.  One  of  the  chief  ways  of  regulating  is  by  means 
of  the  very  small  but  exceedingly  numerous  stomata  (see  § 
79  [4]),  whose  guard  cells  become  turgid  or  collapse  and  so 
determine  the  size  of  the  opening  between  them.  It  has 
been  estimated  that  a  leaf  of  an  ordinary  sunflower  contains 
about  thirteen  million  stomata,  but  the  number  varies  widely 
in  different  plants.  In  ordinary  dorsiventral  leaves  the  sto- 
mata are  much  more  abundant  upon  the  lower  surface  than 
upon  the  upper,  from  which  they  may  be  lacking  entirely. 
In  erect  leaves  they  are  distributed  equally  upon  both  sur- 
faces ;  in  floating  leaves  they  occur  only  upon  the  upper 
surface  ;  in  submerged  leaves  they  are  lacking  entirely. 

The  amount  of  water  thus  evaporated  from  active 
leaves  is  very  great.  It  is  estimated  that  the  leaves  of  a 
sunflower  as  high  as  a  man  evaporate  about  one  quart  of 
water  in  a  warm  day  ;  and  that  an  average  oak  tree  in  its 
five  active  months  evaporates  about  twenty-eight  thousand 
gallons.  If  these  figures  be  applied  to  a  meadow  or  a 
forest  the  result  may  indicate  the  large  importance  of  this 
process. 


302  PLANT   STRDCTDRES 

164.  Photosynthesis. — This  is  the  process  by  which  car- 
bon dioxide  and  water  are  "broken  up,"  their  elements 
recombined  to  form  a  carbohydrate,  and  some  oxygen  given 
off  as  a  waste  product,  the  mechanism  being  the  chloroplasts 
and  light.  It  has  been  sufficiently  described  in  §  55,  and 
also  in  Fla7it  Relations,  pp.  28  and  150. 

165.  Formation  of  proteids. — The  carbohydrates  formed 
by  photosynthesis,  such  as  starch,  sugar,  etc.,  contain  car- 
bon, hydrogen,  and  oxygen.  Out  of  them  the  living  cells 
must  organize  proteids,  and  in  the  reconstruction  nitrogen 
and  sulphur,  and  sometimes  phosphorus,  are  added.  This 
work  goes  on  both  in  green  cells  and  other  living  cells,  as 
it  does  not  seem  to  be  entirely  dependent  upon  chloroplasts 
and  light. 

166.  Transfer  of  carbohydrates  and  proteids. — These  two 
forms  of  food  having  been  manufactured,  they  must  be 
carried  to  the  regions  of  growth  or  storage.  In  order  to  be 
transported  they  must  be  in  soluble  form,  and  if  not  already 
soluble  they  must  be  digested,  insoluble  starch  being  con- 
verted into  soluble  sugar,  etc.  In  these  digested  forms 
they  are  transported  to  regions  where  work  is  going  on, 
and  there  they  are  assimilated— that  is,  transformed  into 
the  enormously  complex  working  substance  protoplasm  ; 
or  they  are  transported  to  regions  of  storage  and  there  they 
are  reconverted  into  insoluble  storage  forms,  as  starch,  etc. 

These  foods  pass  through  both  the  cortex  and  phloem 
in  every  direction,  but  the  long-distance  transfer  of  pro- 
teids, as  from  leaves  to  roots,  seems  to  be  mainly  through 
the  sieve  vessels. 

RESPIRATION 

167.  Respiration. — This  is  an  essential  process  in  plants 
as  well  as  in  animals,  and  is  really  the  phenomenon  of 
"breathing."  The  external  indication  of  the  process  is 
the  absorption  of  oxygen  and  the  giving  out  of  carbon  di- 
oxide ;  and  it  goes  on  in  all  organs,  day  and  night.     When 


PLANT   PHYSIOLOGY  303 

it  ceases  death  ensues  sooner  or  later.  By  this  process 
energy,  stored  up  by  the  processes  of  nutrition,  is  liberated, 
and  with  this  liberated  energy  the  plant  works.  It  may  be 
said  that  oxygen  seems  to  have  the  power  of  arousing  pro- 
toplasm to  activity. 

It  is  not  sufficient  for  the  air  containing  oxygen  to  come 
in  contact  merely  with  the  outer  surface  of  a  complex  plant, 
as  its  absorption  and  transfer  would  be  too  slow.  There 
must  be  an  "internal  atmosphere"  in  contact  with  the 
living  cells.  This  is  provided  for  by  the  intercellular 
spaces,  which  form  a  labyrinthine  system  of  passageways, 
opening  at  the  surface  through  stomata  and  lenticels  (pores 
through  bark).  In  this  internal  atmosphere  the  exchange 
of  oxygen  and  carbon  dioxide  is  effected,  the  oxygen  being 
renewed  by  diffusion  from  the  outside,  and  the  carbon 
dioxide  finally  escaping  by  diffusion  to  the  outside. 

MOVEMENT 

168.  Introductory. — In  addition  to  movements  of  mate- 
rial, as  described  above,  plants  execute  movements  depend- 
ent upon  the  activity  of  protoplasm,  which  result  in  change 
of  position.  Naked  masses  of  protoplasm,  as  the  Plas- 
modium of  slime-moulds  (see  §  51),  advance  with  a  sliding, 
snail-like  movement  upon  surfaces  ;  zoospores  and  ciliated 
sperms  swim  freely  about  by  means  of  motile  cilia ;  while 
many  low  plants,  as  Bacteria  (§  52),  Diatoms  (§  34),  Oscil- 
laria  (§  20),  etc.,  have  the  power  of  locomotion. 

When  the  protoplasm  is  confined  within  rigid  walls  and 
tissues,  as  in  most  plants,  the  power  of  locomotion  usually 
disappears,  and  the  plants  are  fixed  ;  but  within  active  cells 
the  protoplasm  continues  to  move,  streaming  back  and 
forth  and  about  within  the  confines  of  the  cell. 

In  the  case  of  complex  plants,  however,  another  kind 
of  movement  is  apparent,  by  which  parts  are  moved  and 
variously  directed,  sometimes  slowly,  sometimes  with  great 


304 


PLANT   STRUCTURES 


rapidity.  In  these  cases  the  part  concerned  develops  a 
curvature,  and  by  various  curvatures  it  attains  its  ultimate 
position.  These  curvatures  are  not  necessarily  permanent, 
for  a  perfectly  straight  stem  results  from  a  series  of  cur- 
vatures near  its  apex.  Curvatures  may  be  developed  by 
unequal  growth  on  the  two  sides  of  an  organ,  or  by  unequal 
turgidity  of  the  cells  of  the  two  sides,  or  by  the  unequal 
power  of  the  cell  walls  to  absorb  water. 

169.  Hygroscopic  movements. — These  movements  are  only 
exhibited  by  dry  tissues,  and  hence  are  not  the  direct  result 
of  the  activity  of  protoplasm.  The  dry  walls  absorb  mois- 
ture and  swell  up,  and  if  this  absorption  of  moisture  and 
its  evaporation  is  unequal  on  two  sides  of  an  organ  a  curva- 
ture will  result.  In  this  way  many  seed  vessels  are  rup- 
tured, the  sporangia  of  ferns  are  opened,  the  operculum  of 
mosses  is  lifted  off  by  the  peristome,  the  hair-like  pappus 
of  certain  Composites  is  spread  or  collapsed,  certain  seeds 
are  dispersed  and  buried,  etc.  One  of  the  peculiarities  of 
this  hygroscopic  power  of  certain  cells  is  that  the  result 
may  be  obtained  through  the  absorption  of  the  moisture  of 
the  air,  and  the  hygroscopic  awns  of  certain  fruits  have 
been  used  in  the  manufacture  of  rough  hygrometers 
("  measures  of  moisture  "). 

170.  Growth  movements. — Growth  itself  is  a  great  physi- 
ological subject,  but  certain  movements  which  accompany 
it  are  referred  to  here.  Two  kinds  of  growth  movements 
are  apparent. 

One  may  be  called  nutation,  by  which  is  meant  that  the 
growing  tip  of  an  organ  does  not  advance  in  a  straight 
line,  but  bends  now  toward  one  side,  now  toward  the  other. 
In  this  way  the  tip  describes  a  curve,  which  may  be  a 
circle,  or  an  ellipse  of  varying  breadth  ;  but  as  the  tip  is 
advancing  all  the  time,  the  real  curve  described  is  a  spiral 
with  circular  or  elliptical  cross-section.  The  sweep  of  a 
young  hop-vine  in  search  of  support,  or  of  various  tendrils, 
may  be  taken  as  extreme  illustrations,  but  in  most  cases 


PLANT   rilYSlOLOGY  305 

the  nutation  of  growing  tips  only  becomes  apparent  through 
prolonged  experiment. 

The  other  prominent  growth  movement  is  that  which 
places  organs  in  proper  relations  for  their  work,  sending 
roots  into  the  soil  and  stems  into  the  air,  and  directing 
leaf  planes  in  various  ways.  For  example,  in  the  germina- 
tion of  an  ordinary  seed,  in  whatever  direction  the  parts 
emerge  the  root  curves  toward  the  soil,  the  stem  turns 
upward,  and  the  cotyledons  spread  out  horizontally. 

The  movement  of  nutation  seems  to  be  due  largely  to 
internal  causes,  while  the  movements  which  direct  organs 
are  due  largely  to  external  causes  known  as  stinniU.  Some 
of  the  prominent  responses  to  stimuli  concerned  in  direct- 
ing organs  are  as  follows  : 

Heliotropism. — In  this  case  the  stimulus  is  light,  and 
under  its  influence  aerial  parts  are  largely  directed.  Plants 
growing  in  a  window  furnish  plain  illustration  of  helio- 
tropism. In  general  the  stems  and  petioles  curve  toward 
the  light,  showing  positive  heliotropism  (Fig.  279);  the 
leaf  blades  are  directed  at  right  angles  to  the  rays  of  light, 
showing  transverse  lieliotropism  ;  while  if  there  are  hold- 
fasts or  aerial  roots  they  are  directed  away  from  the  light, 
showing  negative  heliotropism.  The  thallus  bodies  of  ferns, 
liverworts,  etc.,  are  transversely  heliotropic,  as  ordinary 
leaves,  a  position  best  related  to  chlorophyll  work.  If  the 
light  is  too  intense,  leaves  may  assume  an  edgewise  or  pro- 
file position,  a  condition  well  illustrated  by  the  so-called 
"compass  plants."     (See  Plant  Belations,  p.  10.) 

Geotropism. — In  this  case  the  stimulus  is  gravity,  and 
its  influence  in  directing  the  parts  of  plants  is  very  great. 
All  upward  growing  plants,  as  ordinary  stems,  some  leaves, 
etc.,  are  negativehj  geotropic,  growing  away  from  the  center 
of  gravity.  Tap-roots  are  notable  illustrations  of  positive 
geotropism,  growing  toward  the  source  of  gravity  with  con- 
siderable force.  Lateral  branches  from  a  main  or  tap-root, 
however,  are  usually  transversrhj  geotropic. 


Fig.  279.  Sunflower  stems  with  tlie  upper  part  of  the  stem  sharply  bent  toward  the 
light,  giving  the  leaves  better  exposure,  the  stem  showing  positive  heliotropism. — 
After  ScHArrNER. 


PLANT   PHYSIOLOGY  30Y 

That  these  influences  in  directing  are  very  real  is  testi- 
fied to  by  the  fact  that  when  the  organs  are  turned  aside 
from  their  proper  direction  they  will  curve  toward  it  and 
overcome  a  good  deal  of  resistance  to  regain  it.  Although 
these  curvatures  are  mainly  developed  in  growing  parts, 
even  mature  parts  which  have  been  displaced  may  be 
brought  back  into  position.  For  example,  when  the  stems 
of  certain  plants,  notably  the  grasses,  have  been  prostrated 
by  wind,  etc.,  they  often  can  resume  the  erect  position  under 
the  influence  of  negative  geotropism,  a  very  strong  and  even 
angular  curvature  being  developed  at  certain  joints. 

Hydrotropism. — The  influence  of  moisture  is  very  strong 
in  directing  certain  organs,  notably  absorbing  systems. 
Roots  often  wander  widely  and  in  every  direction  under 
the  guidance  of  hydrotropism,  even  against  the  geotropic 
influence.  Ordinarily  geotropism  and  hydrotropism  act  in 
the  same  direction,  but  it  is  interesting  to  dissociate  them 
so  that  they  may  "  pull  "  against  one  another.  For  such 
an  experiment  see  Plant  Relations,  p.  91. 

Other  stimuli. — Other  outside  stimuli  which  have  a 
directive  influence  upon  organs  are  chemical  substances 
(chemotropism),  such  as  direct  sperms  to  the  proper  female 
organ  ;  heat  {thermotropism)  ;  water  currents  (rheotropism) ; 
mechanical  contact,  etc.  The  most  noteworthy  illus- 
trations of  the  effect  of  contact  are  furnished  by  tendril- 
climbers.  When  a  nutating  tendril-  comes  in  contact  with 
a  support  a  sharp  curvature  is  developed  which  grasps  it. 
In  many  cases  the  irritable  response  goes  further,  the  ten- 
dril between  the  plant  axis  and  the  support  developing  a 
spiral  coil. 

171.  Irritable  movements. — The  great  majority  of  plants 
can  execute  movements  only  in  connection  with  growth,  as 
described  in  the  preceding  section,  and  when  mature  their 
parts  are  fixed  and  incapable  of  further  adjustment.  Cer- 
tain plants,  however,  have  developed  the  power  of  moving 
mature  parts,  the  motile  part  always  being  a  leaf,  such  as 


308 


PLANT  STRUCTURES 


foliage  leaf,  stamen,  etc.  It  is  interesting  to  note  that  these 
movements  have  been  cultivated  by  but  few  families,  nota- 
ble among  them  being  the  Legumes  (§  141). 

These  movements  of  mature  organs,  some  of  which  are 
very  rapid,  are  due  to  changes  in  the  turgidity  of  cells.  As 
already  mentioned  (§  157),  turgid  cells  are  inflated  and 
rigid,  and  when  turgidity  ceases  the  cells  collapse  and  the 
tissue  becomes  flaccid.  A  special  organ  for  varying  tur- 
gidity, known  as  the  pulvinus,  is  usually  associated  with 
the  motile  leaves  and  leaflets.  The  pulvinus  is  practically 
a  mass  of  parenchyma  cells,  whose  turgidity  is  made  to  vary 
by  various  causes,  and  leaf -movement  is  the  result. 

The  causes  which  induce  some  movements  are  unknown, 
as  in  the  case  of  Desmodium,  gyrans  (see  Plant  Belations, 
p.  49),  whose  small  lateral  leaflets  uninterruptedly  de- 
scribe circles,  completing  a  cycle  in  one  to  three  minutes. 

In  other  cases  the  inciting  cause  is  the  change  from  light 
to  dark,  the  leaves  assuming  at  night  a  very  dif- 
ferent position  from  that  during  the  day.     Dur- 
ing the  day  the  leaflets  are  spread  out  freely, 


Fig.  280.  A  leaf  of  a  sensitive  plant  in  two  conditions:  in  tlie  figure  to  the  left  the  leaf 
is  fully  expanded,  with  its  four  main  divisions  and  numerous  leaflets  well  spread; 
in  the  figure  to  the  right  is  shown  the  same  leaf  after  it  has  heen  "  shocked  "  by 
a  sudden  touch,  or  by  sudden  heat,  or  in  some  other  way;  the  leaflets  have  been 
thrown  together  forward  and  upward,  the  four  main  divisions  have  been  moved 
together,  and  the  main  leaf-stalk  has  been  directed  sharply  downward.— After 

DUCUARTRK. 


PLANT   PHYSIOLOGY  309 

while  at  night  they  droop  and  usually  fold  together  (see 
Plant  Relations,  pp.  9,  10).  These  are  the  so-called  nycti- 
trojnc  movements  or  "  night  movements,"  which  maybe  ob- 
served in  many  of  the  Legumes,  as  clover,  locust,  bean,  etc. 
In  still  other  cases,  mechanical  irritation  induces  move- 
ment, as  sudden  contact,  heat,  injury,  etc.  Some  of  the 
"  carnivorous  plants  "  are  notable  illustrations  of  this,  es- 
pecially Dionoia,  which  snaps  its  leaves  shut  like  a  steel 
trap  when  touched  (see  Plant  Relations,  p.  161).  Among 
the  most  irritable  of  plants  are  the  so-called  "sensitive 
plants,"  species  of  Mimosa,  Acacia,  etc.,  all  of  them  Le- 
gumes. The  most  commonly  cultivated  sensitive  plant  is 
Mimosa  pudira  (Fig.  280),  whose  sensitiveness  to  contact 
and  rapidity  of  response  are  remarkable  (see  Plant  Rela- 
tions, p.  48). 

EEPEODUCTION" 

172.  Reproduction. — The  important  function  of  repro- 
duction has  been  considered  in  connection  with  the  various 
plant  grouj^s.  Among  the  lowest  plants  the  only  method 
of  reproduction  is  cell  division,  which  in  the  complex 
forms  results  in  growth.  In  the  more  complex  plants  va- 
rious outgrowths  or  portions  of  the  body,  as  gemmse,  buds, 
bulbs,  tubers,  various  branch  modifications,  etc.,  furnish 
means  of  propagation.  All  of  these  methods  are  included 
under  the  head  of  vegetative  multiplication,  as  the  plants 
are  propagated  by  ordinary  vegetative  tissues. 

When  a  special  cell  is  organized  for  reproduction,  dis- 
tinct from  the  vegetative  cells,  it  is  called  a  spore,  and  re- 
production hy  spores  is  introduced.  The  first  spores  devel- 
oped seem  to  have  been  those  produced  by  the  division  of 
the  contents  of  a  mother  cell,  and  are  called  asexual  spores. 
These  spores  are  scattered  in  various  ways — by  swimming 
(zoospores),  by  floating,  by  the  wind,  by  insects. 

Another  type  of  spore  is  the  sexual  spore,  formed  by 
the  union  of  two  sexual  cells  called  gametes.  The  gametes 
38 


310  PLANT   STKUCTUKES 

seem  to  have  been  derived  from  asexual  spores.  At  first 
the  pairing  gametes  are  alike,  but  later  they  become  differ- 
entiated into  sperms  or  male  cells,  and  eggs  or  female  cells. 

With  the  establishment  of  alternation  of  generations, 
the  asexual  spores  are  restricted  to  the  sporopliyte,  and  the 
gametes  to  the  gametopliyte.  With  the  further  introduction 
of  heterospory ,  the  male  and  the  female  gametes  are  sepa- 
rated upon  difEerent  gametophytes,  which  become  much 
reduced. 

With  the  reduction  of  the  functioning  megaspores  to 
one  in  a  sporangium  (ovule),  and  its  retention,  the  seed  is 
organized,  and  the  elaborate  scheme  of  insect-pollination 
is  developed. 


CHAPTER  XVII 

PLANT     ECOLOGY 

173.  Introductory. — Ecology  lias  to  do  with  the  external 
relations  of  plants,  and  forms  the  principal  snbjcct  of  the 
volume  entitled  Plant  Belations,  which  should  be  consulted 
for  fuller  descriptions  and  illustrations.  It  treats  of  the 
adjustment  of  plants  and  their  organs  to  their  physical 
surroundings,  and  also  their  relations  with  one  another 
and  with  animals,  and  has  sometimes  been  called  "plant 
sociology." 

LIFE    RELATIONS 

174.  Foliage  leaves. — The  life  relation  essential  to  foliage 
leaves  is  the  relation  to  light.  This  is  shown  by  their 
positions  and  forms,  as  well  as  by  their  behavior  when 
deprived  of  light.  This  light  relation  suggests  the  answer 
to  very  many  questions  concerning  leaves.  It  is  not  very 
important  to  know  the  names  of  different  forms  and  differ- 
ent arrangements  of  leaves,  but  it  is  important  to  observe 
that  these  forms  and  arrangements  are  in  response  to  the 
light  relation. 

In  general  a  leaf  adjusts  its  own  position  and  its  relation 
to  its  fellows  so  as  to  receive  the  greatest  amount  of  light. 
Upon  erect  stems  the  leaves  occur  in  vertical  rows  which 
are  uniformly  spaced  about  the  circumference.  If  these 
rows  are  numerous  the  leaves  are  narrow ;  if  they  are  few 
the  leaves  are  usually  broad.  If  broad  leaves  were  associ- 
ated with  numerous  rows  there  would  be  excessive  shading  ; 

311 


312  PLANT   STRUCTURES 

if  narrow  leaves- were  associated  with  few  rows  there  woiiVl 
be  waste  of  space. 

It  is  very  common  to  observe  the  lower  leaves  of  a  stLin 
long-petioled,  those  above  short-petioled,  and  so  on  nutil 
the  uppermost  have  sessile  blades,  thus  thrusting  the  blades 
of  lower  leaves  beyond  the  shadow  of  the  upper  leaves. 
There  may  also  be  a  gradual  change  in  the  size  and  direc- 
tion of  the  leaves,  the  lower  ones  being  relatively  large  and 
horizontal,  and  the  upper  ones  gradually  smaller  and  more 
directed  upward.  In  the  case  of  branched  (compound) 
leaves  the  reduction  in  the  size  of  the  upper  leaves  is  not 
so  necessary,  as  the  light  strikes  between  the  upper  leaflets 
and  reaches  those  below. 

On  stems  ex2)osed  to  light  only  or  chiefly  on  one  side, 
the  leaf  blades  are  thrown  to  the  lighted  side  in  a  variety 
of  ways.  In  ivies,  many  prostrate  stems,  horizontal  branches 
of  trees,  etc.,  the  leaves  brought  to  the  lighted  side  are 
observed  to  form  regular  mosaics,  each  leaf  interfering 
with  its  neighbor  as  little  as  possible. 

There  is  often  need  of  protection  against  too  intense 
light,  against  chill,  against  rain,  etc.,  which  is  provided 
for  in  a  great  variety  of  ways.  Coverings  of  hairs  or  scales, 
the  profile  position,  the  temporary  shifting  of  position, 
rolling  up  or  folding,  reduction  in  size,  etc.,  are  some  of 
the  common  methods  of  protection. 

175.  Shoots. — The  stem  is  an  organ  which  is  mostly 
related  to  the  leaves  it  bears,  the  stem  with  its  leaves  being 
the  shoot.  In  the  foliage-bearing  stems  the  leaves  must  be 
displayed  to  the  light  and  air.  Such  stems  may  be  sub- 
terranean, prostrate,  floating,  climbing,  or  erect,  and  all  of 
these  positions  have  their  advantages  and  disadvantages, 
the  erect  type  being  the  most  favorable  for  foliage  display. 

In  stems  which  bear  scale  leaves  no  light  relation  is 
necessary,  so  that  such  shoots  may  be  and  often  are  sub- 
terranean, and  the  leaves  may  overlap,  as  in  scaly  buds 
and  bulbs.     The  subterranean  position  is  very  favorable 


PLANT  ECOLOGY  313 

for  food  storage,  and  such  shoots  often  become  modified  as 
food  depositories,  as  in  bulbs,  tubers,  rootstocks,  etc.  In 
the  scaly  buds  the  structure  is  used  for  protection  rather' 
than  storage. 

The  stem  bearing  floral  leaves  is  the  shoot  ordinarily 
called  ''the  flower,"  whose  structure  and  work  have  been 
sufliciently  described.  Its  adjustments  have  in  view  polli- 
nation and  seed  dispersal,  two  very  great  ecological  sub- 
jects full  of  interesting  details. 

176.  Roots. — Eoots  are  absorbent  organs  or  holdfasts  or 
both,  and  they  enter  into  a  variety  of  relations.  Most 
common  is  the  soil  relation,  and  the  energetic  way  in 
which  such  roots  penetrate  the  soil,  and  search  in  every 
direction  for  water  and  absorb  it,  proves  them  to  be  highly 
organized  members.  Then  there  are  roots  related  to  free 
water,  and  others  to  air,  each  with  its  appropriate  struc- 
ture. More  mechanical  are  the  clinging  roots  (ivies,  etc.), 
and  prop  roots  (screw  pines,  banyans,  etc.),  but  their  adap- 
tation to  the  peculiar  service  they  render  is  none  the  less 
interesting. 

The  above  statements  concerning  leaves,  shoots,  and 
roots  should  be  applied  with  necessary  modifications  to  the 
lower  plants  which  do  not  produce  such  organs.  The 
light  relation  and  its  demands  are  no  less  real  among  the 
Algfe  than  among  Spermatophytes,  as  well  as  relations  to 
air,  soil,  water,  mechanical  support,  etc. 

PLANT    ASSOCIATIONS 

177.  Introductory, — Plants  are  not  scattered  at  hap- 
hazard over  the  surface  of  the  earth,  but  are  organized  into 
definite  communities.  These  communities  are  determined 
by  the  conditions  of  living — conditions  which  admit  some 
plants  and  forbid  others.  Such  an  assemblage  of  plants 
living  together  in  similar  conditions  is  a  plant  m^snriafiait. 
Closely  related  plants  are  the  most  intense  rivals,  as  they 


314  PLANT  STEUCTURES 

make  almost  identical  demands  upon  their  surroundings. 
Hence  it  is  usual  for  a  plant  association  to  be  made  up  of  a 
large  number  of  unrelated  plants. 

There  are  numerous  factors  which  combine  to  deter- 
mine associations,  and  it  is  known  as  yet  only  in  a  vague  way 
how  they  operate. 

178.  Ecological  factors. —  Wafer. — This  is  a  very  impor- 
tant factor  in  the  organization  of  associations,  which  are 
usually  local  assemblages.  Taking  plants  altogether,  the 
amount  of  water  to  which  they  are  exposed  varies  from 
complete  submergence  to  perpetual  drought,  but  M'ithin 
this  range  plants  vary  widely  as  to  the  amount  of  water 
necessary  for  living. 

Heat. — In  considering  the  general  distribution  of  plants 
over  the  surface  of  the  earth,  great  zones  of  plants  are  out- 
lined by  zones  of  temperature ;  but  in  the  organization  of 
local  associations  in  any  given  area  the  temperature  condi- 
tions are  nearly  uniform.  Usually  plants  work  only  at 
temperatures  between  32°  and  122°  Fahr.,  but  for  each 
plant  there  is  its  own  range  of  temperature,  sometimes 
extensive,  sometimes  restricted.  Even  in  plant  associations, 
however,  the  effect  of  the  heat  factor  may  be  noted  in  the 
succession  of  plants  through  the  working  season,  spring- 
plants  being  very  different  from  summer  and  autumn 
plants. 

Soil. — The  great  importance  of  this  factor  is  evident, 
even  in  water  plants,  for  the  soil  of  the  drainage  area  deter- 
mines the  materials  carried  by  the  water.  Soil  is  to  be 
considered  both  as  to  its  chemical  composition  and  its 
physical  properties,  the  latter  chiefly  in  reference  to  its 
disposition  toward  water.  Soils  vary  greatly  in  the  power 
of  receiving  and  retaining  water,  sand  having  a  high  recep- 
tive and  low  retentive  power,  and  clay  just  the  reverse, 
and  these  factors  have  large  effect  upon  vegetation. 

Light. — All  green  plants  can  not  receive  the  same  amount 
of  light.     Hence  some  of  them  have  learned  to  live  with  a 


PLANT   ECOLOGY  315 

less  amount  than  others,  and  are  "  shade  plants "  as  dis- 
tinct from  "  light  plants."  In  forests  and  thickets  many 
of  these  shade  plants  are  to  be  seen  which  would  find  an 
exposed  situation  hard  to  endure.  In  almost  every  associa- 
tion, therefore,  plants  are  arranged  in  strata,  dependent 
upon  the  amount  of  light  they  receive,  and  the  number  of 
these  strata  and  the  plants  characterizing  each  stratum  are 
important  factors  to  note. 

Wind. — This  is  an  important  factor  in  regions  where 
there  are  strong  prevailing  winds.  Wind  has  a  drying 
effect  and  increases  the  transpiration  of  plants,  tending  to 
impoverish  them  in  water.  In  such  conditions  only  those 
plants  can  live  which  are  well  adapted  to  regulate  trans- 
piration. 

The  above  five  factors  are  among  the  most  important, 
but  no  single  factor  determines  an  association.  As  each 
factor  has  a  large  possible  range,  the  combinations  of  fac- 
tors may  be  very  numerous,  and  it  is  these  combinations 
which  determine  associations.  For  convenience,  however, 
associations  are  usually  grouped  on  the  basis  of  the  water 
factor,  at  least  three  great  groups  being  recognized. 

179.  Hydrophyte  associations. — These  are  associations  of 
water  plants,  the  water  factor  being  so  conspicuous  that  the 
plants  are  either  submerged  or  standing  in  water.  A  plant 
completely  exposed  to  water,  submerged,  or  floating,  may 
be  taken  to  illustrate  the  usual  adaptations.  The  epi- 
dermal walls  are  thin,  so  that  water  may  be  absorbed 
through  the  whole  surface ;  hence  the  root  system  is  very 
commonly  reduced  or  even  wanting  ;  and  hence  the  water- 
conducting  tissues  (xylem)  are  feebly  developed.  The  tis- 
sues for  mechanical  support  (stereome)  are  feebly  devel- 
oped, the  plant  being  sustained  by  the  buoyant  power  of 
water.  Such  a  plant,  although  maintaining  its  form  in 
water,  collapses  upon  removal.  Very  common  also  is  the 
development  of  conspicuous  air  passages  for  internal  aera- 
tion and  for  increasing  buoyancy  ;  and  sometimes  a  special 


316  PLANT   STRL'CTUKES 

buoyancy  is  provided  for  Ly  the  development  of  bladder- 
like floats. 

Conspicuous  among  hydrophyte  associations  may  be 
mentioned  the  following :  (1)  Free-swimming  associations, 
in  which  the  plants  are  entirely  sustained  by  Avater,  and  are 
free  to  move  either  by  locomotion  or  by  water  currents. 
Here  belong  the  "plankton  associations,"  consisting  of 
minute  plants  and  animals  invisible  to  the  naked  eye, 
conspicuous  among  the  plants  being  the  diatoms ;  also  the 
"•  pond  associations,"  composed  of  algje,  duckweeds,  etc., 
which  float  in  stagnant  or  slow-moving  waters. 

(2)  Pondweed  associations,  in  which  the  plants  are  an- 
chored, but  their  bodies  are  submerged  or  floating.  Here 
belong  the  "  rock  associations,"  consisting  of  plants  an- 
chored to  some  firm  support  under  water,  the  most  conspic- 
uous forms  being  the  numerous  fresh-water  and  marine 
alg^e,  among  which  there  are  often  elaborate  systems  of 
holdfasts  and  floats.  The  "  loose-soil  associations  "  are  dis- 
tinguished by  imbedding  their  roots  or  root-like  processes 
in  the  mucky  soil  of  the  bottom  (Figs.  281,  282).  The  wa- 
ter lilies  with  their  broad  floating  leaves,  the  pondweeds  or 
pickerel  weeds  with  their  narrow  submerged  leaves,  are 
conspicuous  illustrations,  associated  with  which  are  algae, 
mosses,  water  ferns,  etc. 

(3)  Swamp  associations,  in  which  the  plants  are  rooted 
in  water,  or  in  soil  rich  in  water,  but  the  leaf-bearing  stems 
rise  above  the  surface.  The  conspicuous  swamp  associations 
are  "reed  swamps,"  characterized  by  bulrushes,  cat-tails 
and  reed-grasses  (Figs.  283,  284),  tall  wand-like  Monocoty- 
ledons, usually  forming  a  fringe  about  the  shallow  margins 
of  small  lakes  and  ponds;  '' swamp-moors,"  the  ordinary 
swamps,  marshes,  bogs,  etc.,  and  dominated  by  coarse 
sedges  and  grasses  (Fig.  282) ;  "swamp-thickets,"  consist- 
ing of  willows,  alders,  birches,  etc. ;  "  sphagnum-moors,"  in 
which  sphagnummoss  predominates,  and  is  accompanied  by 
numerous  peculiar  orchids,  heaths,  carnivorous  plants,  etc.  ; 


PLANT   ECOLOGY 


319 


"swamp-forests,"  which  are  largely  coniferous,  tamarack 
(larch),  pine,  hemlock,  etc.,  prevailing. 


180.  Xerophyte  associations. — These  associations  are  ex- 
posed to  the  other  extreme  of  the  water  factor,  and  are  com- 
posed of  plants  adapted  to  dry  air  and  soil.     To  meet  these 


320 


PLANT   STRUCTURES 


drought  conditions  numerous  adaptations  have  been  de- 
veloped and  are  very  characteristic  of  xerophytic  plants. 
Some  of  the  conspicuous  adaptations  are  as  f  oUoavs  :  peri- 


odic reduction  of  surface,  annuals  bridging  over  a  period 
of  drought  in  the  form  of  seeds,  geophilous  plants  also  dis- 
appearing from  the  surface  and  persisting  in  subterranean 


324:  PLANT   STEUCTUEES 

parts,  deciduous  trees  and  shrubs  dropping  their  leaves, 
etc.  ;  temporary  reduction  of  surface,  the  leaves  rolling  up 
or  folding  together  in  various  ways ;  profile  position,  the 
leaves  standing  edgewise  and  not  exposing  their  flat  sur- 
faces to  the  most  intense  light ;  motile  leaves  which  can 
shift  their  position  to  suit  their  needs  ;  small  leaves,  a  very 
characteristic  feature  of  xerophytic  plants ;  coverings  of 
hair ;  dwarf  growth ;  anatomical  adaptations,  such  as 
cuticle,  palisade  tissue,  etc.  Probably  the  most  conspicu- 
ous adaj)tation,  however,  is  the  organization  of  "water- 
reservoirs,"  which  collect  and  retain  the  scanty  water  sup- 
ply, doling  it  out  as  the  plant  needs  it. 

Some  of  the  prominent  associations  are  as  follows : 
"rock-associations,"  composed  of  plants  living  upon  exposed 
rock  surfaces,  walls,  fences,  etc.,  notably  lichens  and  mosses  ; 
"sand  associations,"  including  beaches,  dunes,  and  sandy 
fields ;  "  shrubby  heaths,"  characterized  by  heath  plants ; 
"  plains,"  the  great  areas  of  dry  air  and  wind  developed  in 
the  interiors  of  continents ;  "  cactus  deserts,"  still  more 
arid  areas  of  the  Mexican  region,  where  the  cactus,  agave, 
yucca,  etc.,  have  learned  to  live  by  means  of  the  most  ex- 
treme xerophytic  modifications  ;  "  tropical  deserts,"  where 
xerophytic  conditions  reach  their  extreme  in  the  combina- 
tion of  maximum  heat  and  minimum  water ;  "  xerophyte 
thickets,"  the  most  impenetrable  of  all  thicket-growths, 
represented  by  the  "  chaparral  "  of  the  Southwest,  and  the 
"  bush  "  and  "  scrub  "  of  Africa  and  Australia ;  "  xero- 
phyte forests,"  also  notably  coniferous.  (See  Figs.  285, 
286,  287.) 

181.  Mesophyte  associations. — Mesophytes  make  up  the 
common  vegetation,  the  conditions  of  moisture  being  me- 
dium, and  the  soil  fertile.  This  is  the  normal  plant  condi- 
tion, and  is  the  arable  condition — that  is,  best  adapted  for 
the  plants  which  man  seeks  to  cultivate.  If  a  hydrophytic 
area  is  to  be  cultivated,  it  is  drained  and  made  mesophytic  ; 
if  a  xerophytic  area  is  to  be  cultivated,  it  is  irrigated  and 


39 


5   a 


PLANT  ECOLOGY  337 

made  mesophytic.  As  contrasted  with  hydrophyte  and 
xerophyte  associations,  the  mesophyte  associations  are  far 
riclier  in  leaf  forms  and  in  general  luxuriance.  The  arti- 
ficial associations  which  have  been  formed  under  the  influ- 
ence of  man,  through  the  introduction  of  weeds  and  culture 
plants,  are  all  mesophytic. 

Among  the  mesophyte  grass  and  herb  associations  are 
the  "  arctic  and  alpine  carpets,"  so  characteristic  of  high 
latitudes  and  altitudes  where  the  conditions  forbid  trees, 
shrubs,  or  even  tall  herbs ;  "  meadows,"  areas  dominated  by 
grasses,  the  prairies  being  the  greatest  meadows,  where 
grasses  and  flowering  herbs  are  richly  displayed ;  "  pas- 
tures," drier  and  more  open  than  meadows. 

Among  the  woody  mesophyte  associations  are  the  "thick- 
ets," composed  of  willow,  alder,  birch,  hazel,  etc.,  either 
pure  or  forming  a  jungle  of  mixed  shrubs,  brambles,  and 
tall  herbs  ;  ''  deciduous  forests,"  the  glory  of  the  temperate 
regions,  rich  in  forms  and  foliage  display,  with  annual  fall 
of  leaves,  and  exhibiting  the  remarkable  and  conspicuous 
phenomenon  of  autumnal  coloration;  " rainy  tropical  for- 
ests," in  the  region  of  trade  winds,  heavy  rainfalls,  and 
great  heat,  where  the  world's  vegetation  reaches  its  climax, 
and  where  in  a  saturated  atmosphere  gigantic  Jungles  are 
developed,  composed  of  trees  of  various  heights,  shrubs  of 
all  sizes,  tall  and  low  herbs,  all  bound  together  in  an  inex- 
tricable tangle  by  great  vines  or  lianas,  and  covered  by  a 
luxuriant  growth  of  numerous  epiphytes.  (See  Figs.  288, 
289.) 


GLOS  S AR Y 


[The  definitions  of  a  glossary  are  often  unsatisfactory.  It  is  much  better  to  con- 
sult the  fuller  explanations  of  the  text  by  means  of  the  index.  The  following  glos- 
sary includes  only  frequently  recurring  technical  terms.  Those  which  are  found  only 
in  reasonably  close  association  with  their  explanation  are  omitted.  The  number  fol- 
lowing each  definition  refers  to  the  page  where  the  term  will  be  found  most  fully 
defined.] 


AcTiNOMORPHic  :  applied  to  a  flower  in  which  the  parts  in  each  set  are 

similar ;  regular.     228. 
Akene  :  a  one-seeded  fruit  which  ripens  dry  and  seed-like.    212. 
Alternation  op  generations  :   the  alternation  of  gametophyte  and 

sporophyte  in  a  life  history.     94. 
Anemophilous  :  applied  to  flowers  or  plants  which  use  the  wind  as  agent 

of  pollination.     181. 
Anisocarpic  :  applied  to  a  flower  whose  carpels  are  fewer  than  the  other 

floral  organs.     268. 
Anther  :  the  sporangium-bearing  part  of  a  stamen.     197. 
Antheridium  :  the  male  organ,  producing  sperms.     16. 
Antipodal  cells  :  in  Angiosperms  the  cells  of  the  female  gametophyte 

at  the  opposite  end  of  the  embryo-sac  from  the  egg-apparatus. 

205. 
Apetalous  :  applied  to  a  flower  with  no  petals.     221. 
Apocarpous  :  applied  to  a  flower  whose  carpels  are  free  from  one  an- 
other.    226. 
Archegonium  :  the  female,  egg-producing  organ  of  Bryophytes,  Pteri- 

dophytes,  and  Gymnosperms.     100. 
Arohesporium  :  the  first  cell  or  group  of  cells  in  the  spore-producing 

series.     102. 
Ascocarp  :  a  special  ease  containing  asci.     58. 
Ascospore  :  a  spore  formed  within  an  ascus.     59. 
Ascus :  a  delicate  sac  (mother-cell)  within  which  ascospores  develop. 

59. 
Asexual  spore  :  one  produced  usually  by  cell-division,  at  least  not  by 

cell-union.     9, 

829 


330  GLOSSARY 

Calyx  :  the  outer  set  of  floral  leaves.    321. 

Capsule  :  in  Bryophytes  the  spore-vessel ;  in  Angiosperms  a  dry  fruit 

which  opens  to  discharge  its  seeds.    98,  211. 
Carpel  :  the  megasporophyll  of  Spermatophytes.     178. 
Chlorophyll  :  the  green  coloring  matter  of  plants.    5. 
Chloroplast  :  the  protoplasmic  body  within  the  cell  which  is  stained 

green  by  chlorophyll.     7. 
Columella  :  in  Bryophytes  the  sterile  tissue  of  the  sporogonium  which 

is  surrounded  by  the  sporogenous  tissue.     106. 
CoNiDiUM  :  an  asexual  spore  formed  by  cutting  off  the  tip  of  the  sporo- 

phore,  or  by  the  division  of  hyphae.     58. 
Conjugation  :  the  union  of  similar  gametes.     15. 
Corolla  :  the  inner  set  of  floral  leaves.     221. 

CoitLEDON  :  the  first  leaf  developed  by  an  embryo  sporophyte.     138. 
Cyclic  :  applied  to  an  arrangement  of  leaves  or  floral  parts  in  which 

two  or  more  appear  upon  the  axis  at  the  same  level,  forming  a  cycle, 

or  whorl,  or  verticil.     159. 

Dehiscence  :  the  opening  of  an  organ  to  discharge  its  contents,  as  in 
sporangia,  pollen-sacs,  capsules,  etc.     199. 

DiCHOTOMOus  :  applied  to  a  style  of  branching  in  which  the  tip  of  the 
axis  forks.    35. 

DicEcious  :  applied  to  plants  in  which  the  two  sex-organs  are  upon  dif- 
ferent individuals.     115. 

DoRsivENTRAL :  applied  to  a  body  whose  two  surfaces  are  differently 
exposed,  as  an  ordinary  thallus  or  leaf.     109. 

Egg  :  the  female  gamete.     16. 

Egg-apparatus  :  in  Angiosperms  the  group  of  three  cells  in  the  embryo- 
sac  composed  of  the  egg  and  the  two  synergids.     204. 
Elater  :  in  Liverworts  a  spore-mother-cell  peculiarly  modified  to  aid 

in  scattering  the  spores.     103. 
Embryo  :  a  plant  in  the  earliest  stages  of  its  development  from  the 

spore.     137. 
Embryo-sac  :  the  megaspore  of  Spermatophytes,  which  later  contains 

the  embryo.     178. 
Endosperm  :  the  nourishing  tissue  developed  within  the  embryo-sac,  and 

thought  to  represent  the  female  gametophyte.     180. 
Endosperm  nucleus  :  the  nucleus  of  the  embryo-sac  which  gives  rise  to 

the  endosperm.     205. 
Entomophilous  :  applied  to  flowers  or  plants  which  use  insects  as  agents 

of  pollination.     196. 


GLOSSARY  331 

Epigynous  :  applied  to  a  flower  whose  outer  parts  appear  to  arise  from 

the  top  of  the  ovary.    235. 
EusPORANGiATE :  applied  to  those  Pteridophytes  and  Spermatophytes 

whose  sporangia  develop  from  a  group  of  epidermal  and  deeper 

cells.     157. 

Family  :  a  group  of  related  plants,  usually  comprising  several  genera. 

236. 
Fertilization  :  the  union  of  sperm  and  egg.     16. 
Filament  :  the  stalk-like  part  of  a  stamen.     197. 
Fission  :    cell  -  division   which    includes    the    wall    of    the    old    cell. 

10. 
Foot  :  in  Bryophytes  the  part  of  the  sporogonium  imbedded  in  the 

gametophore ;  in  Pteridophytes  an  organ  of  the  sporophyte  embryo 

to  absorb  from  the  gametophyte.     98,  138. 

Gametangium  :  the  organ  within  which  gametes  are  produced.     11. 

Gamete  :  a  sexual  cell,  which  by  union  with  another  produces  a  sexual 
spore.     10. 

Gametophore  :  a  special  branch  which  bears  sex  organs.     98. 

Gametophyte  :  in  alternation  of  generations,  the  generation  which  bears 
the  sex  organs.     97. 

Generative  cell  :  in  Spermatophytes  the  cell  of  the  male  gameto- 
phyte (within  the  pollen  grain)  which  gives  rise  to  the  male 
cells.     180. 

Genus  :  a  group  of  very  closely  related  plants,  usually  comprising  sev- 
eral species.     237. 

Haustorium  :  a  special  organ  of  a  parasite  (usually  a  fungus)  for  ab- 
sorption.   50. 

Heterogamous  :  applied  to  plants  whose  pairing  gametes  are  un- 
like.    15. 

Heterosporous  :  applied  to  those  higher  plants  whose  sporophyte  pro- 
duces two  forms  of  asexual  spores.     151. 

Homosporous  :  applied  to  those  plants  whose  sporophyte  produces  simi- 
lar asexual  spores.     151. 

Host  :  a  plant  or  animal  attacked  by  a  parasite.     48. 

HVPHA :  an  individual  filament  of  a  mycelium.     49. 

Hypocotyl  :  the  axis  of  the  embryo  sporophyte  between  the  root-tip  and 
the  cotyledons.     209. 

Hypogynous  :  applied  to  a  flower  whose  outer  parts  arise  from  beneath 
the  ovary.     224. 


332  GLOSSAKY 

Indusium  :  in  Perns  a  flap-like  membrane  protecting  a  sorus.     143. 

Inflorescence  :  a  flower-cluster.    230. 

Insertion  :  the  point  of  origin  of  an  organ.    234. 

Integument  :  in  Spermatophytes  a  membrane  investing  the  nucellus. 

178. 
Involucre  :  a  cycle  or  rosette  of  bracts  beneath  a  flower-cluster,  as  in 

Umbellifers  and  Composites.     275. 
Isocarpic  :  applied  to  a  flower  whose  carpels  equal  in  number  the  other 

floi'al  organs.     268. 
IsoGAMOUs  :  applied  to  plants  whose  pairing  gametes  are  similar.     15. 

Leptosporangiate  :  applied  to  those  Ferns  whose  sporangia  develop 
from  a  single  epidermal  cell.     157. 

Male  cell  :  in  Spermatophytes  the  fertilizing  cell  conducted  by  the 

pollen-tube  to  the  egg.     180. 
Megasporangium  :  a  sporangium  which  produces  only  megaspores.   152. 
Megaspore  :  in  heterosporous  plants  the  large  spore  which  produces  a 

female  gametophyte.     152. 
MEGASPOROPnYLL  :  a  sporophyll  which  produces  only  megasporangia. 

152. 
Mesophyll  :  the  tissue  of  a  leaf  between  the  two  epidermal  layers  which 

usually  contains  chloroplasts.     141. 
MicRospoRANGiUM  :   a  sporangium  which  produces  only  microspores. 

152. 
Microspore  :  in  heterosporous  plants  the  small  spore  which  produces  » 

male  gametophyte.     152. 
Microsporophyll  :  a  sporophyll  which  produces  only  microsporangia. 

152. 
Micropyle:  the  passageway  to  the  nucellus  left  by  the  integument. 

178. 
Moncecious  :  applied  to  plants  in  which  the  two  sex  organs  are  upon 

the  same  individual.     115. 
MoNOPODiAL :  applied  to  a  style  of  branching  in  which  the  branches 

arise  from  the  side  of  the  axis.     35. 
Mother  cell  :  usually  a  cell  which  produces  new  cells  by  internal  divi- 
sion.   9. 
Mycelium  :  the  mat  of  filaments  which  composes  the  working  body  of 

a  fungus.    49. 

Naked  flower  :  one  with  no  floral  leaves.    222. 
Nucellus  :  the  main  body  of  the  ovule.     178. 


GLOSSARY  333 

Oogonium  :  the  female,  egg-producing  organ  of  Thallophytes.     16. 

OosPHERE  :  the  female  gamete,  or  egg.     16. 

Oospore  :  the  sexual  spore  resulting  from  fertilization.     16. 

Ovary  :  in  Angiosperms  the  bulbous  part  of  the  pistil,  which  contains 

the  ovules.     199. 
Ovule  :  the  megasporangium  of  Spermatophytes.     178. 

Pappus  :  the  modified  calyx  of  the  Composites.    278. 

Parasite  :  a  plant  which  obtains  food  by  attacking  living  plants  or  ani- 
mals.   48. 

Pentacyclic  :  applied  to  a  flower  whose  four  floral  organs  are  in  five 
cycles,  the  stamens  being  in  two  cycles.    268. 

Perianth  :  the  set  of  floral  leaves  when  not  differentiated  into  calyx 
and  corolla.    221. 

Perigynous  :  applied  to  a  flower  whose  outer  parts  arise  from  a  cup 
surrounding  the  ovary.     225. 

Petal  :  one  of  the  floral  leaves  which  make  up  the  corolla.    221. 

Photosynthesis  :  the  process  by  which  chloroplasts,  aided  by  light, 
manufacture  carbohydrates  from  carbon  dioxide  and  water.    84. 

Pistil  :  the  central  organ  of  the  flower,  composed  of  one  or  more  car- 
pels.    200. 

Pistillate  :  applied  to  flowers  with  carpels  but  no  stamens.    218. 

Pollen  :  the  microspores  of  Spermatophytes.     174. 

Pollen-tube  :  the  tube  developed  from  the  wall  of  the  pollen  grain 
which  penetrates  to  the  egg  and  conducts  the  male  cells.     180. 

Pollination  :  the  transfer  of  pollen  from  anther  to  ovixle  (in  Gymno- 
sperms)  or  stigma  (in  Angiosperms).     181. 

Polypetalous  :  applied  to  flowers  whose  petals  are  free  from  one  an- 
other.   227. 

Prothallium  :  the  gametophyte  of  Ferns.     130. 

Protonema  :  the  thallus  portion  of  the  gametophyte  of  Mosses.    98. 

Radial  :  applied  to  a  body  with  uniform  exposure  of  surface,  and  pro- 
ducing similar  organs  about  a  common  center.     120. 

Receptacle  :  in  Angiosperms  that  part  of  the  stem  which  is  more  or 
less  modified  to  support  the  parts  of  the  flower.     222. 

Rhizoid  :  a  hair-like  process  developed  by  the  lower  plants  and  by  inde- 
pendent gametophytes  to  act  as  a  holdfast  or  absorbing  organ,  or 
both.     109. 

Saprophyte  :  a  plant  which  obtains  food  from  the  dead  bodies  or  body 
products  of  plants  or  animals.    4S. 


334  GLOSSARY 

Scale  :  a  leaf  without  chlorophyll,  and  usually  reduced  in  size. 
161. 

Sepal  :  one  of  the  floral  leaves  which  make  up  the  calyx.    231. 

Seta  :  in  Bryophytes  the  stalk-like  portion  of  the  sporogonium.    98. 

Sexual  spore  :  one  produced  by  the  union  of  gametes.     10. 
■Species  :  plants  so  nearly  alike  that  they  all  might  have  come  from  a 
single  parent.    287. 

Sperm  :  the  male  gamete.     16. 

Spiral  :  applied  to  an  arrangement  of  leaves  or  floral  parts  in  which 
no  two  appear  upon  the  axis  at  the  same  level ;  often  called  alter- 
nate.    193. 

Sporangium  :  the  organ  within  which  asexual  spores  are  produced  (ex- 
cept in  Bryophytes).     10. 

Spore  :  a  cell  set  apart  for  reproduction.    9. 

Sporogonium  :  the  leafless  sporophyte  of  Bryophytes.    98. 

Sporophore  :  a  special  branch  bearing  asexual  spores.    49. 

Sporophyll  :  a  leaf  set  apart  to  produce  sporangia.     145. 

Sporophyte  :  in  alternation  of  generations,  the  generation  which  pro- 
duces the  asexual  spores.     97. 

Stamen  :  the  microsporophyll  of  Spermatophytes.     174. 

Staminate  :  applied  to  a  flower  with  stamens  but  no  carpels.     218. 

Stigma  :  in  Angiosperms  that  portion  of  the  carpel  (usually  of  the  style) 
prepared  to  receive  pollen.     199. 

Stoma  (pi.  Stomata)  :  an  epidermal  organ  for  regulating  the  communi- 
cation between  green  tissue  and  the  air.     141. 

Strobilus  :  a  cone-like  cluster  of  sporophylls.     161. 

Style:  the  stalk-like  prolongation  from  the  ovary  which  bears  the 
stigma.     199. 

Suspensor  :  in  heterosporous  plants  an  organ  of  the  sporophyte  embryo 
which  places  it  in  a  more  favorable  position  in  reference  to  food 
supply.     168. 

Symbiont:  an  organism  which  enters  into  the  condition  of  symbio- 
sis.    79. 

Symbiosis  :  usually  applied  to  the  condition  in  which  two  different 
organisms  live  together  in  intimate  and  mutually  helpful  rela- 
tions.    79. 

Sympetalous  :  applied  to  a  flower  whose  petals  have  coalesced. 
227. 

Syncarpous  :  applied  to  a  flower  whose  carpels  have  coalesced. 
226. 

Synergid  :  in  Angiosperms  one  of  the  pair  of  cells  associated  with  the 
egg  to  form  the  egg-apparatus.     204. 


GLOSSAEY  335 

Testa  :  the  hard  coat  of  the  seed.     184. 

Tetracyclic  :  applied  to  a  flower  whose  four  floral  organs  are  in  four 

cycles.    268. 
Tetrad  :  a  group  of  four  spores  produced  by  a  mother-cell.     103. 

Zoospore  :  a  motile  asexual  spore.     10. 

Zygomorphic  :  applied  to  a  flower  in  which  the  parts  in  one  or  more 

sets  are  not  similar  ;  irregular.    229. 
Zygote  :  the  sexual  spore  resulting  from  conjugation.     15. 


INDEX 


[The  italicized  nnmbers  indicate  that  the  subject  is  ilhistrated  upon  the  page  cited. 
In  such  case  the  subject  may  be  referred  to  only  in  the  illustration,  or  it  may  be 
referred  to  also  in  the  text.] 


Absorption,  299. 

Acacia,  265. 

Aconitum,  261. 

Acorus,  219,  243. 

Actinomorphy,  228. 

Adder's  tongue  :  see  Ophioglossmn. 

Adiantum,  143,  145. 

^cidiomycetes,  50,  62. 

-ZEcidiospore,  66. 

^cidium,  66. 

Agaricus,  68,  69. 

Agave,  247. 

Air  pore :  see  Stoma, 

Akene,  212,  213,  214,  216,  277. 

Alcbemilla,  225. 

Alder :  see  Alnus. 

Algaj,  4,  5,  17. 

Alisma,  210,  240. 

Almond :  see  Primus. 

Alnus,  257. 

Alternation    of    generations,    94. 

129. 
Amaryllidaceje,  247. 
Amaryllis   family:   see   Araarylli- 

dacea?. 
Ambrosia,  279. 
Anient,  257. 
Anaptychia,  81,  S2. 


Anemophilous,  181. 
Angiosperms,  173,  195,  217. 
Anisocarpa%  268. 
Annulus,  136,  146,  150. 
Anther,  190,  197,  199. 
Antheridium,  16,  99,  100,  112,  121, 

133,  134,  161,  166. 
Antherozoid,  16. 

Anthoceros,  104,  105,  111,  116,  118 
Anthophytes,  172. 
Antipodal  cells,  202,  205,  208. 
Antirrhinum,  228,  275. 
Ant-plants,  90,  91. 
Apical  cell,  134. 
Apical  group,  283. 
Apium,  267. 
Apocarpy,  199,  222,  225. 
Apocynaceje,  271. 
Apocynum,  272. 
Apogamy,  131. 
Apospory,  132. 
Apothecium,  79,  81,  82. 
Apple :  see  Pirus. 
Aquilegia,  198. 
Aracea?,  248. 
Araliaeeai,  267. 
Araucaria,  190. 
Arbor  vitfe :  see  Thuja. 
Arbutus,  198 :  see  Epigjea. 
Archegoniates,  101. 
337 


338 


INDEX 


Archegonium,  99, 100,  IIS,  II4, 133, 

135,  161,  167,  179. 
Archesporiuin,  102,  IO4,  105,  146. 
Archichlamydeie,  255. 
Arctostaphylos,  269. 
Areolae,  111,  114. 
Arisa?ma,  243,  244. 
Arnica,  275,  276,  278. 
Aroids,  243. 
Artemisia,  279. 
Arum,  2J^5. 
Ascocarp,  58,  59.  - 
Aseomyeetes,  50,  57. 
Ascospore,  59. 
Ascus,  59. 
Asexual  spore,  9. 
Aspidium,  130,  136,  144 
Assimilation,  302. 
Aster,  279. 
Astragalus,  265. 
Atherosperma,  198. 
Azalea,  270. 

B 

Bacillus,  76. 

Bacteria,  21,  75.  76. 

Balm :  see  Melissa. 

Banana,  I40. 

Bark,  284,  289. 

Basidiomycetes,  50,  68 

Basidiospore,  69,  72. 

Basidium,  69,  71. 

Bean :  see  Phaseolus. 

Bearberry :  see  Arctostaphylos. 

Beech,  2.56. 

Bellis,  279. 

Berberis,  19S. 

Bidens,  278. 

Beggar-ticks,  213. 

Bignonia,  211. 

Birch,  256. 

Blackberry :  see  Rubus. 


Black  knot,  60. 
Black  mould,  52. 
Blasia,  116. 

Blueberry :  see  Vacciniura. 
Blue-green  algae,  6,  17. 
Blue  mould,  60. 
Boletus,  73,  74. 
Botrychium,  145,  I49. 
Botrydium,  2S. 
Box  elder,  234. 
Bracket  fungus,  72. 
Brake :  see  Pteris. 
Brassiea,  261. 
Bryophytes,  2,  93,  172. 
Brown  alga?,  6,  '32. 
Bryum,  120,  124. 
Buckeye,  235. 
Butomus,  199. 

Buttercup :  see  Ranunculus. 
Buttercup   family :  see   Ranuncu 
lace*. 

C 

Cabbage :  see  Brassiea. 

Calamus  :  see  Acorus. 

Calla-lily,  243. 

Callithamnion,  43. 

Callophyllis,  39. 

Call  una,  270. 

Calopogon,  249. 

Caltha,  260. 

Calycanthus,  226,  261. 

Calypso,  249. 

Calyptra,  102,  125. 

Calyptrogen,  293. 

Calyx,  220,  221. 

Cambium,  285,  287,  288. 

Capsella,  209,  293. 

Capsule,  98,  123,  125,  126,  211,  212. 

Caraway :  see  Carum. 

Carbohydrate,  302. 

Carbon  dioxide,  83. 


INDEX 


339 


Carnivorous  plants,  92. 

Carpel,  177,  178,  199,  219,  220. 

Carpi  nus,  217,  258. 

Carpospore,  44^  45. 

Carrot :  see  Daucus. 

Carum,  267. 

Cassia,  265. 

Cassiope,  269. 

Castilleia,  275. 

Catkin,  257. 

Catnip :  see  Nepeta. 

Cat-tail :  see  Typha. 

Cattleya,  254. 

Caulicle,  209. 

Cauline,  166. 

Cedar  apple,  67,  68. 

Celery:  see  Apiuiu. 

Cell,  6,  7. 

Cellulose,  7. 

Cercis,  265. 

Chalazogamy,  258,  259. 

Characeae,  4G- 

Chemotropism,  307. 

Cherry :  see  Primus. 

Chestnut,  256. 

Chlorophycese,  6,  21. 

Chlorophyll,  5,  83. 

Chloroplast,  7,  8. 

Chrysanthemum,  279. 

Cilia,  10. 

Circinate,  136,  143. 

Cladophora,  25. 

Clavaria,  73. 

Climbing  fern  :  see  Lygodiuni. 

Closed  bundle,  290. 

Clover :  see  Trifoliura. 

Club  mosses,  162. 

Cnieus,  278. 

Cocklebur :  see  Xanthium. 

Ccenocyte,  27. 

Coleochaete,  106,  J07. 

Collateral  bundle,  287. 


CoUenchyma,  284. 

Columella,  104,  105,  106,  126. 

Compass  plant:  see  Silphium. 

Compositaj,  275. 

Composites,  275,  276,  277,  278. 

Concentric  bundle,  292. 

Conferva  forms,  22. 

Conidia,  58,  60. 

Conifers,  191,  282, 

Conium,  267. 

Conjugate  forms,  31. 

Conjugation,  15. 

Connective,  196. 

Conocephalus,  111. 

Convolvulacea%  271. 

Convolvulus  forms,  270. 

Convolvulus,  273, 

Coprinus,  70. 

Coral  fungus,  73,  74. 

Coreopsis,  278. 

Coriandrum,  267. 

Cork,  284. 

Corn,  216,  282,  290. 

Cornaceae,  267. 

Corolla,  220,  221. 

Cortex,  283,  284,  288. 

Cotton,  206. 

Cotyledon,  137,  138,  168,  184,  ^09, 

210,  216,  217. 
Cranberry:  see  Vaccinium. 
Crataegus,  262. 
Crocus,  249. 
Crucifer,  262. 
Crucifera%  262. 
Cryptogams,  172, 
Cunila,  274. 
Cup  fungus,  60,  61. 
Cupule,  112,  114. 
Cyanophycese,  6,  17. 
Cycads,^i<95,  186,  187,  189. 
Cyclic,  1*59,  193. 
Cyperacea?,  241. 


340 


INDEX 


Cypripedium,  249,  253. 
Cystocarp,  43,  44- 
Cystopteris,  7S,  I44. 
Cytoplasm,  7. 

D 

Daisy:  see  Bellis. 

Dandelion :  see  Taraxacum. 

Dasya,  40- 

Datura,  197. 

Daucus,  S66,  267. 

Dead-nettle,  228. 

Definitive  nucleus :  see  Endosperm 

nucleus. 
Dehiscence,  lOS,  199. 
Delphinium,  260,  261. 
Dermatogen,  2S3. 
Desmids,  31,  32. 
Desmodium,  308. 
Diatoms,  45- 
Dichotomous,  35. 
Dicotyledons,  208,  233,  254,  282. 
Differentiation,  3,  280. 
Dogbane:  see  Apocynum. 
Dog-tooth  violet:  see  Erythronium. 
Dogwood  family:  see  Cornacea^ 
Dorsiventral.  109. 
Downy  mildew,  55. 
Drupe,  264. 
Digestion,  802. 
Dioecious,  115. 
Disk,  276,  277. 
Dodder,  S6. 

E 

Ear-fungus,  74. 
Easter  lily,  221. 
Ecology,  297,  311. 
Economic  botany,  297. 
Ectocarpus,  33. 
Edogonium,  22,  £3. 
Egg,  16,  202,  204,  205,  206. 


Egg-apparatus,  204,  205,  206. 

Elater,  103,  113,  US. 

Elm :  see  Ulmus. 

Embryo,  137, 167, 168, 170, 183, 207, 

208,  209,  210,  211. 
Embryo-sac,  178,  179,201,203,208. 
Endosperm,  179,  180,  207,  208,  211. 
Endosperm  nucleus,  202,  205. 
Entomophilous,  196. 
Epidermis,  141,  142,  191,  283,  284, 

295. 
Epiga^a,  269. 
Epigyny,  224,  225. 
Epilobium,  212. 
Epiphyte,  157. 
Equisetales,  159. 
Equisetum,  159,  160,  161. 
Ergot,  60.  61. 
Erica,  270. 
Ericaceae,  268. 
Erigenia,  267. 
Erythronium,  250. 
pjusporangiate,  157. 
Evolution,  3. 

F 

Fennel :  see  Foeniculum. 

Ferns,  155,  156. 

Fertilization,  16,  181,  206,  207. 

Festuca,  24O. 

Figwort    family :    see    Scrophula- 

riaceap. 
Filament,  8.  196,  197. 
Filicales,  155. 
Fireweed  :  see  Epilobium. 
Fission,  10. 
Flax :  see  Linum. 
Floral  leaves,  218. 
Floridea?,  38. 
Flower,  218. 
Flowering  plants,  172. 
Foeniculum,  267. 


INDEX 


341 


Foliar,  166. 

P^od,  83,  299. 

Foot,  98,  102,  137,  138,  168. 

Fragiiria,  JU,  227,  262. 

Fruit,  211,  212,  213,  214,  ^15. 

Fucus,  35,  37. 

Funaria,  99,  102,  121,  124, 1^5, 126. 

Fungi,  4,  48. 

G 

Gametangium,  11. 

Gamete,  10,  13. 

Gainetophore,  98,  112,  120,  124. 

Gametophyte,  97,  107, 132, 134, 161, 

166,  167,  176,  179,  180,  201,  203, 

204,  ^05. 
Gaultheria,  270. 
Gaylussacia,  269. 
Gemma,  112,  114. 
Generative  cell,  180,  201. 
Gentianacea?,  271. 
Geophilous,  246. 
Geotropism,  305. 
Gerardia,  275. 
Germination,  187,  214. 
Gigartina,  38. 
Gills,  71. 
Ginkgo,  191. 
Gladiolus,  249,  251. 
Gleditsehia,  236,  265.' 
Gloeocapsa,  17,  IS. 
Glume,  241. 

Goldenrod :  see  Solidago. 
Gonatonema,  31. 
Graminejp,  241. 
Green  algne,  6.  21. 
Green  plants,  88. 
Green  slimes,  20. 
Grimmia.  126. 
Growth  movement,  304. 
Growth  ring,  234. 
Grain,  241. 

40 


Grasses,  240. 

Grass  family:  see  Gramineae. 
Gymnosperms,  171,  173,  195. 
Gymnosporangium,  67. 

H 

Habenaria,  249,  252. 

Harebell,  228. 

Haustoria,  50. 

Hazel :  see  Carpinus. 

Heart-wood,  289. 

Heat,  314. 

Heath  family :  see  Ericaceae. 

Heaths,  268,  269,  270. 

Helianthus,  279,  285,  306. 

Heliotropism,  305. 

Hemiarcyria,  75. 

Hemlock :  see  Conium. 

Henbane :  see  Hyoscyamus. 

Hepaticae,  109. 

Heterocyst,  18. 

Heterogamy,  15. 

Heterospory,  151. 

Hickory,  256. 

Hippuris,  283. 

Homospory,  151. 

Honey  locust :  see  Gleditsehia. 

Horehound:  see  Marrubium. 

Hornbeam :  see  Carpinus. 

Horsetail,  159. 

Host,  48. 

Huckleberry :  see  Gaylussacia. 

Hydnum,  73,  74. 

Hydra,  90. 

Hydrophytes,  6.  315. 

Hydrophytum,  91, 

Hydrotropism,  307. 

Hygroscopic  movement,  304. 

Hyoscyamus,  196. 

Hypha,  49. 

Hypocotyl,  184,  209,  216,  217. 


342 


INDEX 


Hypodermis,  284. 
Hypogyny,  224,  225. 
Hyssopus,  274. 

I 

Indigo :  see  Indigofera. 

Indigofera,  265. 

ludusium,  136,  143,  lU- 

Inflorescence,  280. 

Insects  and  flowers,  90. 

Integument,  178,  179,  201, 202,  203. 

Involucre,  i'67,  275,^77. 

Ipomoea,  228,  270. 

Iridacese,  247. 

Iris,  248,  251. 

Iris  family :  see  Iridaeeae. 

Irritable  movement,  307. 

Isocarpa",  268. 

Isoetes,  169. 

Isogamy,  15. 


Japan  lily,  24S. 

Jungermannia,  105,  115,  116,  117. 

Juniper,  19^. 


K 


Kiilmia,  270. 


Labiatae,  272. 

Tiabiates,  272. 

Lactuca,  279. 

Laminaria,  33,  5^. 

Lamium,  274.  275. 

Larcli  :  see  Larix. 

Larix,  192. 

Larkspur :  see  Delphinium. 

Laurel :  see  Kalmia. 

Lavandula,  275. 

Leaf,  141,  142,  295.  296,  311. 

Legumes,  250,  251,  264. 

Leguminosa?,  264. 


Lemna,  201. 

Lepidozia,  117. 

Lepiota,  70. 

Leptosporangiate,  157. 

Lettuce :  see  Lactuca. 

Leueanthemum,  279. 

Liatris,  278. 

Lichens,  77,  78,  79,  87. 

Life  relations,  811. 

Light,  814. 

Ligule,  168. 

Liliacea?,  246. 

Lilies,  245. 

Lilium,  203,  204,  ^05,  207,  224,  2^9, 

295. 
Lily :  see  Lilium. 
Lily  family :  see  Liliaceaj. 
Linaria,  228,  275. 
Linum,  220. 
Liverworts,  109. 
Loculus,  200. 
Locust :  see  Robinia. 
Lotus,  264. 
Lupin  us,  265. 
Lycopersicum,  275. 
Lycopodiales,  162. 
Lycopodium,  162,  163. 
Lygodium,  145. 
Lyonia,  269. 

M 

Macrospore,  152. 

Maidenhair  fern  :  see  Adiantum. 

Male  cell,  180,  181, 201,  206,  207. 

Maple,  212. 

jMarasmius,  70. 

Marchantia,  IO4, 110,  111,  112,  113, 

114. 
Marguerite :  see  Leueanthemum. 
^NLarjoram  :  see  Origanum. 
IMarrubium,  275. 
;\[arsli  marigold:  see  Caltha. 


INDEX 


343 


Marsilia,  15S. 

Megasporangium,  152,  177,  179. 
Megaspore,  152,  105,  167,  179,  201, 

203. 
Megasporophyll,  152, 165,  177,  199. 
Melissa,  275. 
Mentha,  229,  274. 
Meristem,  281. 

Mesophyll,  141,  lj!f2,  191,  295. 
Mesophytes,  324. 
Mestome,  282. 

Micropyle,  178,  201,  202,  206. 
Microspira,  76. 
Microspha?ra,  58. 
Microsporangium,  152,  176,  197. 
Microspore;  152,  165,  166,  179,  197, 

201. 
Microsporophyll,  152,  i65,  174,196, 

198. 
Midrib,  234. 
Mildews,  57. 
Mimosa,  265,  308,  809. 
Mint :  see  Mentha. 
Mint  family  :  see  Labiatae. 
Monocotyledons,  208,  232,  236, 289. 
Monoecious,  115. 
Monopodia],  35. 
Monotropa,  270. 
Moonwort:  see  Botrychium. 
Morels,  60,  62. 

Morning-glory :  see  Ipomoea. 
Morphology,  297. 
Mosses,  93,119,  124. 
Mother  cell,  9. 
Mougeotia,  31. 
Movement,  303. 
Mucor,  49,  52,  53,  54,  55. 
Mullein :  see  Verbascum. 
Musci,  119. 
Mushrooms,  68. 

Mustard  family :  see  Cruciferfe. 
Mycelium,  49. 


Mycomycetes,  50. 

Mycorrhiza,  87,  88. 
Myristica,  214. 
Myrmecophytes,  90,  91. 
Myxomycetes,  74,  75. 

N 
Naias,  237. 
Narcissus,  247. 
Nemalion,  4^. 
Nepeta,  275. 
Nicotiana,  227,  275. 
Nightshade  family :  see  Solanacea?. 
NTostoc,  18. 

Nucellus,  178,  179,  201,  202,  203. 
Nucleus,  7. 
Nutation,  304. 
Nutmeg,  214. 
Nutrition,  3,  299. 
Nyctitropic  movement,  309. 
Nyraphaeaceaj,  261. 

0 

Oak,  255,  256. 

CEdogonium :  see  Edogonium. 

Onoclea,  145,  I47, 148. 

Oogonium,  16. 

Oosphere,  16. 

Oospore,  16,  101. 

Open  bundle,  287. 

Operculum,  122,  125. 

Ophioglossum,  145,  149. 

Orchidacea?,  249. 

Orchids,  249,  252,  253.  254. 

Orchid  family :  see  Orchidaceaei 

Origanum,  274. 

Ornithogalum,  247. 

Oscillatoria.  19. 

Osmunda,  145.  156. 

Ostrich  fern  :  see  Onoclea. 

Ovary,  199,  200,  202. 

Ovule,  178,  179,  201,  203. 


344 


INDEX 


Palisade  tissue,  U2,  295. 

Palmaceffi,  241. 

Palm  family  :  see  Palmaceae. 

Palms,  241,  2^2,  243. 

Papaveraceae,  261. 

Pappus,  276,  277,  278. 

Parasites,  48,  85. 

Parenchyma,  280,  281,  282,  288. 

Parmelia,  79. 

Parsley:  see  Petroselinum. 

Parsley  family :  see  Umbellifera'. 

Parsnip :  see  Pastinaca. 

Parthenogenesis,  52. 

Pastinaca,  267. 

Pathology,  297. 

Pea :  see  Pisum. 

Peach :  see  Prunus. 

Peach  curl,  60. 

Pea  family :  see  Leguminosas. 

Pear :  see  Pirus. 

Peat,  119. 

Peltea,  U6. 

Penicillium,  GO. 

Pentacyclaj,  268. 

Pentstemon,  275. 

Peony,  220. 

Pepper,  211,  258. 

Pepper  family :  see  Piperaceae. 

Perianth,  219,  220,  221. 

Periblem,  283. 

Perigyny,  225,  226. 

Peristome,  126,  127. 

Peronospora,  55,  56. 

Petal,  220,  221. 

Petiole.  141. 

Petroselinum,  267. 

Ph;eophyce;i3,  6,  32. 

Phanerogams,  172. 

Phaseolus,  216,  265. 

Phloem,  285,  287, 288, 290, 292,  291 


Phlox,  228,  271. 

Photosyntas,  84. 

Photosynthesis,  84,  302. 

Phycomycetes,  50,  51. 

Physcia,  79. 

Physiology,  297. 

Picea,  179,  181,  182. 

Pileus,  71. 

Pine :  see  Pinus. 

Pineapple,  215. 

Pinus,  173,  175,  176,  177,  178,  181, 

183,  184,  188,  191,  286. 
Piperaceae,  258. 
Pirus,  225,  262,  263. 
Pistil,  199,  200,  219,  220. 
Pisum,  265. 
Pith,  285,  287,  288. 
Planococcus,  76. 
Plantaginace*,  275. 
Plant  body,  6. 
Plant  associations,  313. 
Plasmodium,  74,  75. 
Plastid,  7,  8. 
Platycerium,  132. 
Plerome,  283. 
Pleurococcus,  21. 
Plum  :  see  Prunus. 
Plumule,  210. 
Pod,  211,  212. 
Pogonia,  249. 
Polemoniaceae,  271. 
Polemonium,  271. 
Pollen,  174,  176,  197,  201. 
Pollen-tube,  179,  180,  181,  187,  202., 

206,  W7. 
Pollination,  181. 
Polyembryony,  183. 
Polymorphism.  63. 
Pol'ypetaly,  226. 
Polyporus,  71,  72. 
Polysiphonia,  44- 
Polytrichum,  96. 


INDEX 


345 


Pome,  263. 

Pondweeds,  237. 

Poplars,  255. 

Popowia,  198. 

Poppy,  261. 

Poppy  family:  see  Papaveracejp. 

Populus,  256. 

Pore-fungus,  72. 

Potamogeton,  237,  SSS. 

Potato :  see  Solanum. 

Potentilla,  225,  262. 

Proteid,  302. 

Prothallium,  130,  132,  134. 

Protococcus  forms,  22. 

Protonema,  95,  98. 

Protoplasm,  7. 

Prunus,  213,  262. 

Pseudomonas,  76. 

Pseudopodium,  105,  123,  124. 

Pteridophytes,  2,  128,  172,  291. 

Pteris,  133,  134,  135,  137,  I4I,  142 

143,  145,  281,  291,  292,  293. 
Ptilota,  42. 

Puccinia,  63,  64,  65,  66. 
Puff-balls,  68,  74. 
Pulvinus,  308. 

Q 

Quillwort :  see  Isoetes. 

R 
Rabdonia,  41- 
Radiate  bundle,  294. 
Radicle,  209. 
Radish,  120. 

Ragweed :  see  Ambrosia. 
Ranunculaceae,  261. 
Ranunculus,  222.  259. 
Raspberry :  see  Rubus. 
Rays,  275,  276. 
Receptacle.  222. 
Red  algaD,  6,  38. 


Redbud :  see  Cercis. 

Redwood :  see  Sequoia. 

Reproduction,  3,  8,  309. 

Respiration,  302. 

Rheotropisni,  307. 

Rhizoid,  109,  110,  134. 

Rhizophores,  I64. 

Rhododendron,  270,  271. 

Rhodophycea\  6,  38. 

Riccia,  104,  110. 

Ricciocarpus,  110. 

Ricinus,  288. 

Robinia,  265. 

Root,  138,  217,  293,  294,  313. 

Root-cap,  293. 

Root-fungus,  87,  88. 

Root-hairs,  217,  300. 

Root-pressure,  300. 

Root-tubercles,  89. 

Rosacea?,  262. 

Rose  family :  see  Rosaceae. 

Rosin-weed :  see  Silphium. 

Rosmarinus,  275. 

Royal  fern :  see  Osmunda. 

Rubus,  262. 

Rumex,  284. 

Rust,  62,  63,  64,  65,  66. 


Sac-fungi,  57. 
Sage :  see  Salvia. 
Sage-brush :  see  Artemisia. 
Sagittaria,  208,  338. 
Salix,  219,  233,  256,  257. 
Salvia,  275. 
Salvinia,  158. 
Saprolegnia,  51,  52. 
Saprophyte,  48,  84. 
Sap-wood,  289. 
Sargassum,  35.  36. 
Saururus,  219,  258. 
Scales,  161. 


346 


INDEX 


Scapania,  116, 
Schizomycetes,  21. 
Schizophytes,  31. 
Sclerenchyma,  2S1,  282,  284,  285, 

288,  290,  291. 
Scouring  rush,  159. 
Scrophulariaceir,  275. 
Scutellaria,  275. 
Sedge  family :  see  Cyperaceap. 
Seed,  183,  184,  210,  211,  212,  214. 
Selaginella,  163,  164.  165,  166,  168. 
Sensitive  fern  :  see  Onoclea. 
Sensitive-plant :  see  Acacia. 
Sepal,  220,  221. 
Sequoia,  189. 
Seta,  98,  125. 
Sex,  12. 

Sexual  spore,  10. 
Shepherd's  purse :  see  Capsella. 
Shield  fern  :  see  Aspidium. 
Shoot,  312. 

Sieve  vessels,  285,  386. 
Silphium,  279. 
Siphon  forms,  27. 
Siphonogaras,  183. 
Siphonogamy,  183. 
Slime  moulds,  74,  75. 
Smut,  62. 

Snapdragon :  see  Antirrhinum. 
Soil,  314. 
Solanacea?,  375. 
Solanum,  198,  275. 
Solidago,  279. 
Solomon's  seal,  233. 
Sorus,  136,  143,  I44. 
Spadix,  244,  245. 
Spathe,  244,  245. 
Sperm,  16,  100,  133,  135,  163,  166, 

169,  187,  190. 
Sperm  at  ia,  43,  44. 
Spermatophytes,  2,  171,  172. 
Spermatozoid,  16. 


Sperm  mother  cell,  100. 

Sphagnum,  105,  106,  122,  123. 

Spike,  240. 

Spira3a,  263. 

Spiral,  193. 

Spirillum,  76. 

Spirogyra,  28,  29,  30. 

Spongy  tissue,  I42. 

Sporangium,  10,  136,  143,  145,  150, 
157,  163,  179. 

Spore,  9. 

Sporidium,  65. 

Sporogenous  tissue,  103. 
Sporogonium,  98, 102,  IO4, 105, 106, 

125,  126. 
Sporophore,  49,  50. 
Sporophyll,  145,  I47,  I48,  149,  174, 

176. 
Sporophyte,  97,  102,  137. 
Spruce  :  see  Picea. 
Stability  of  form,  398. 
Stamen,   174,   176,   196,   198,  219, 

220. 
Stele,  191,  383,  385. 
Stem,  139,  382,  389,  291,  313. 
Stemonitis,  75. 
Stereome,  282,  299. 
Sterile  tissue,  103. 
Sticta,  80. 
Stigma,  199,  202. 
Stomata,  I4I,  I42,  191,  295,  301. 
Strawberry :  see  Pragaria. 
Strobilus,  160,  161,  163,  165,  174, 

175,  176,  193,  194. 
Style,  199,  202. 
Substratum,  49. 
Sumach,  235. 

Sunflower:  see  Helianthus. 
Suspensor,     167,    168,     183,    209, 

210. 
Symbiont,  79,  86. 
Symbiosis,  79,  86. 


INDEX 


347 


Syiupetalir,  268. 
Sympetaly,  226,  227. 
Symplocarpus,  243. 
Syncarpy,  199,  219,  225. 
Synergid,  202,  204,  205,  206. 


Taiiacetum,  279. 
Tansy :  see  Tanacetum. 
Taraxacum,  213,  277,  278. 
Taxonomy,  297. 
Teleutospore,  64,  65. 
Tension  of  tissues,  298. 
Testa,  1S4,  211. 
TetracycLT,  268. 
Tetrad,  103. 
Tetraspore,  43. 
Teucrium,  230,  274,  275. 
Thallophytes,  2,  4,  172. 
Thermotropism,  307. 
Thistle :  see  Cnicus. 
Thorn  apple :  see  Datura. 
Thuja,  193. 

Thymus,  274. 

Tickseed :  see  Coreopsis. 

Tissues,  280. 

Toad-flax :  see  Linaria. 

Toadstools,  68. 

Tobacco :  see  Nicotiana. 

Tomato:  see  Lycopersicum. 

Trachea?,  285,  286. 

Tracheids,  286. 

Transfer  of  water,  300. 

Transpiration,  301. 

Tree  fern,  I40. 

Trichia,  75. 

Tric'hogyne,  43,  44. 

Trillium,  207,  246,  265. 

Truffles,  60. 

Turgidity,  298. 

Typha,  239,  240. 


U 

Umbel,  266,  267. 
Umbellifera?,  2G6. 
Umbellifers,  260. 
Ulmus,  210,  256 
Ulothrix,  12,  13,  22. 
Uredo,  64. 
Uredospore,  63,  64. 

V 

Vaccinium,  269. 

Vascular  bundle,  232, 234, 287, 291. 

Vascular  cylinder,  234,  287. 

Vascular  system,  129,  139. 

Vaucheria,  26,  27,  28. 

Vegetative  multiplication,  9. 

Veins,  141,  142. 

Venation,  233. 

Verbascum,  275. 

Verbenacea^,  275. 

Vernation,  143. 

Vernonia,  279. 

Veronica,  275. 

Vicia,  265. 

Violet,  211,  229. 

W 

Wall  cell,  180. 

Walnut,  256. 

Water,  83,  314. 

Water  ferns,  158. 

Water-lily,  223,  261. 

Water-lily  family :  see  Nympha?a- 

cea3. 
Water  moulds,  51. 
Wheat  rust,  63,  64,  65,  66. 
Willow :  see  Salix. 
Wind,  315. 
Wintergreen :  see  Gaultheria. 


348  INDEX 


Wistaria,  265. 
Witches'-broom,  60. 
Wormwood :  see  Artemisia. 


Xanthiura,  279. 

Xerophytes,  319. 

Xylem,  285,  287,  288,  290,  202,  2U4. 


Yeast,  62. 


Zanuichellia,  237. 
Zoospore,  10. 
Zygomorphy,  228,  229. 
Zygospore,  15. 
Zygote,  15. 


(4) 


THE     END 


TWENTIETH  CENTURY  TEXT-BOOKS  OF  BOTANY. 


By  JOHN  M.  COULTER,  A.M.,  Ph.D., 

Head  of  Department  of  Botany,  University  of  Chicago. 

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they  protect  themselves  from  enemies  of  various  kinds  in  their  struggle  for  existence, 
their  habits  individually  and  in  family  groups,  and  their  relations  to  other  forms  of 
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Plant  Studies.     An  Elementary  Botany.     i2mo.     Cloth, 

This  book  is  designed  for  those  schools  in  which  there  is  not  a  sufficient  allot- 
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Manv  of  the  high  schools  as  well  as  the  smaller  colleges  and  seminaries  that 
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